Check Isuzu pickups, 83-93 or so. The trans behind a G200 (1.9L) or a 4ZD1 (2.3L) should be the same. If you find one with a cable clutch it should be pretty close to drop in, though I have honestly not measured the length on a pickup tranny. The 88 Impulse car 5 Spd I've got is the same length as my 2WD 76 LUV tranny, but it is set up for a hydro clutch so it would be more trouble to make work in an 80 LUV. I believe the 2WD pickup trans will be the same, but already set for the cable clutch. If you see a pickup with a hydro clutch, it will be a bit different trans and likely behind a 2.6L 4ZE1. Not that it wouldn't work, but it would tend to be more different and require more work to bolt it up. Diesels have a different bolt pattern, so the 5spds from them will not work on a G180.
If you are looking for a 4x4 trans then look at 4x pickups and Troopers. The trans is longer though, so driveshaft mods and mount fabrication will be required.
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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
