I am kind of confused what part you are asking about, the front inner fender, the front outer fender, or the rear wheel well tub in the bed?
Body parts are identical from 76-80, 75 and older had some slight changes around the grill, valance, and bumper but are generall still interchangable. The bed parts interchange from 75-80, and I'd bet the fender wells in the bed are still the same 72-80. 4WD and 2WD made no difference in body parts other than an extra hole in the cab floor for the 4wd shifter.
For tips in spotting the year of your donor vehicle check out the sticky thread at the top of Stock Trucks.
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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)
MEPR: Man, my 4x4 makes all other LUVs look good
