76-82 are a direct fit in LUVs, and Isuzus for a few years after that. I think in about 84 Isuzu started putting the 1.9L motor in instead of the 1.8L so as long as it is a 1.8L G180 and not a 1.9L G200 the head from a newer Isuzu will fit.
There is one minor issue you might have to worry about. If your current motor has a mechanical fuel pump bolted to the head on the front right side, the hole won't be there on some older heads. The casting and bolt holes will be there through so it just needs some material removed and it would work.
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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
