The only possible difference is in the clutch but it is minor. In 79 they used a smaller clutch disc so the flywheel is slightly different, the disc, and the pressure plate. In 80 the 4x4s got the larger disc, and in 81 2wd and 4wds got it. I think the release bearing is the same though, and the pilot bearing and shaft splines on the tranny are. Just don't try to mix disc/plate/flywheel parts between the two, and if possible go with the stuff from an 81 so you get the bigger clutch.
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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
