There are no spelling problems, since /p/ is spelled <p> or <pp> in all cases, and similarly /d/ is <d> or <dd>.
Since this contrast is between a voiceless and a voiced consonant, there are various differences that become more apparent when the sound is final, for instance vowel length as in beep/bead and devoicing of a nasal in cramp/crammed. I have treated as minimal the contrast between final /ps/ as in types and final /dz/ as in tides, since the difference in pronunciation of the -s ending is more or less neutralised in normal speech. (See paper by Merwyn Torikian, "Watch your language: an account of Soundedit with reference to the validity of phonological rules" in System 20, 4, pages 471 - 480, November 1992, in which he demonstrates with waveforms and sonograms that the plural marker after a voiced consonant is often realised as /s/ while the corresponding voiceless plural marker is often realised as /z/). I have left in the pair instep/instead, though these words differ in stress as well as sound.
The contrast is unlikely to be a problem for any learner. Even German speakers who devoice closing /d/ would still be unlikely to confuse carp and card.The most interesting pair is tenpences/tendencies. Note how this is non-minimal in normal speech since the first /n/ in tenpences will be assimilated to /m/. Other interesting pairs include:
couple cuddle
harpist hardest
oppress address
pivot divot
upper udder
whelping welding
The density value is 3.1%. The list makes 323 semantic contrasts, a loading of 62%.
ape aid aping aiding apple addle apples addles beep bead bleep bleed bleeping bleeding bump bummed burp bird cap cad carp card carping carding chap Chad chip chid chump chummed clamp clammed clap clad coop cooed cop cod cope code coping coding copes codes copied codded copping codding Corp cawed Corp chord Corp cord Corp cored couple cuddle coupled cuddled couples cuddles coupling cuddling cp CD cramp crammed creep creed croup crewed croup crude cup cud damp dammed dep dead deep deed dip did dupe dude dupes dudes gap gad gawp gaud gawp gored grape grade grapes grades grape grayed grape greyed grip grid grips grids grippe greed gulp gulled hap had harp hard harper harder harpist hardest harpy hardy heap he'd heap heed heaping heeding help held hemp hemmed hep head hip hid hoop who'd hop hod hops hods hope hoed hump hummed instep instead jape jade keep keyed kip kid kipping kidding kopecks codex lamp lambed lamp lammed lap lad leap lead leaping leading leaps leads limp limbed limp limned lip lid lope load lopes loads loping loading lope lode lopes lodes lope lowed map mad mop mod mope mode mopes modes mope mowed MP MD nape neighed neap knead neap need nope node op odd opium odium opp odd oppress address oppressed addressed oppresses addresses oppressing addressing overripe override P D P's D's pace dace packer Dacca packer Dakar pad Dad pads Dads paddy Daddy pail dale pails dales pain Dane pains Danes pain deign pained deigned paining deigning pains deigns pair dare paired dared pairing daring pairs dares pale dale pales dales pallid dallied pally dally Pam dam Pam damn pamper damper pampers dampers pan Dan pander dander pane Dane panes Danes pane deign panes deigns pap pad pare dare pared dared pares dares paring daring park dark parka darker parky Darky part dart parted darted parting darting parts darts pate date pates dates pause daws pause doors pave Dave paw daw paws daws paw door paws doors pawn dawn pawned dawned pawning dawning pawns dawns pay day pays days pays daze pea D peas D's peal deal pealing dealing peals deals pear dare pears dares pease D's peck deck pecked decked pecker decker peckers deckers pecking decking pecks decks pee D peel deal peeler dealer peelers dealers peeling dealing peelings dealings peels deals peep peed peer dear peers dears peer deer pees D's pelf delf pelt dealt pen den pens dens pence dense penny Denny peri deary peris dearies perk dirk perks dirks pert dirt Perth dearth pet debt pets debts pew dew pew due pews dues pi Di pi die pi dye pick Dick picker dicker pickers dickers pie Di pie die pies dies pie dye pies dyes pied died pied pipe pier dear piers dears pier dear pier deer pig dig pigging digging pigs digs pike dike pikes dikes pike dyke pikes dykes pill dill pimple dimple pimpled dimpled pimples dimples pin din pinning dinning pins dins pine dine pined dined pines dines pining dining pine dyne pines dynes pitch ditch pitched ditched pitches ditches pitching ditching pity ditty pities ditties pivot divot pivots divots pixie dixie pixies dixies plop plod plopping plodding plops plods plump plumbed pock dock pocked docked pocks docks pocket docket pocketed docketed pocketing docketing pockets dockets podgy dodgy pole dole poles doles poll dole polled doled polling doling polls doles poll doll polls dolls Polly dolly poly dolly polys dollies pond donned poodle doodle poodles doodles pooh do poor dour poorly dourly pop pod popping podding pops pods Pope dope Popes dopes pore daw pores daws pore door pores doors porn dawn porter daughter porters daughters pose does pose dohs pose doze posed dozed poses dozes posing dozing posies dozes posses dosses post dosed pot dot potted dotted pots dots potting dotting potty dotty pottier dottier pottiest dottiest pound downed pour daw pours daws pour door pours doors pout doubt pouted doubted pouting doubting pouts doubts power dower powered dowered powering dowering powers dowers pox docks praise drays pram drachm prams drachms pram dram prams drams prank drank prawn drawn pray dray prays drays press dress pressed dressed presses dresses pressing dressing pressings dressings prey dray preys drays pride dried prima dreamer prink drink prinking drinking prinks drinks prior drier priors driers prise dries prize dries prole droll prone drone prop drop propped dropped propping dropping props drops prop prod propping prodding props prods prows drowse Pru drew pry dry pried dried pries dries prying drying pub dub pubs dubs puce deuce puck duck pucks ducks pug Doug pug dug pugs dugs puke duke pukes dukes pump dump pumped dumped pumping dumping pumps dumps pun done pun dun punned dunned punning dunning puns duns punk dunk punks dunks purge dirge purges dirges pursed durst pyorrhoea diarrhoea pyre dire pyre dyer pyres dyers pyxes dixies quip quid quips quids ramp rammed rape raid rapes raids raping raiding rape rayed reap read reaper reader reapers readers reaping reading reaps reads reap reed reaps reeds rep read rep red repp read repp red repress redress repressed redressed represses redresses repressing redressing rip rid ripping ridding rips rids ripe ride riper rider Ripon ridden ripple riddle rippled riddled ripples riddles rippling riddling rope road rope rode rope rowed ropeway roadway ropeways roadways sap sad sapling saddling sapper sadder scarp scarred seep cede seeping ceding seeps cedes seep seed seeping seeding seeps seeds sepia seedier shape shade shapes shades shaping shading sharp shard sheep she'd shop shod sip Sid skimp skimmed skip skid skipping skidding skips skids slip slid sloop slewed slope slowed slump slummed snipe snide snoop snood soap sewed soap sowed sop sod sopping sodding sops sods steep steed step stead steppe stead stoep stood stripe stride stripes strides sump summed sweep swede tenpences tendencies thump thumbed tippler tiddler tipplers tiddlers tope toad topes toads tope toed tope towed topi toady topis toadies topple toddle toppled toddled topples toddles toppling toddling trap trad tripe tried troop trued troupe trued type tide type tied typing tiding upper udder uppers udders VP VD warp ward warping warding warps wards warp warred weep we'd weep weed weeping weeding weeps weeds whelp weld whelping welding whelps welds whelp welled whoop who'd whoopee woody whop wad whopping wadding wipe wide wiper wider yelp yelled