78 or 79 ? Minor changes to interior trim, round gauges instead of of egg shaped, and different texture on the gauge cluster and glove box door. Side vent design changed to match. Ducting was added from the blower to these vents and the wind driven foot vents were eliminated. The seat belts also changed in 78 or 79 to use a different latch. They are not compatible with older belt buckles. The button on the latch became square instead of round with this change. viewtopic.php?f=5&t=2083
1979 First official year of 4x4 model. This was the first 4x4 production vehicle (according to what I've read) with IFS. Nothing major changed other than the unknowns between 78 or 79 above. 4x4 models have a different torsion bar configuration to go along with the front axle. Changes were made to the frame mounts for the torsion bars and axle.
1980 Basically the same as 1979, I believe the 4x4 dash light was added (but that might be a Mikado option from 79). There is a minor change to the side marker lights, the mounting and lenses are slightly different. The voltage regulator connector is round as opposed to squarish, but I'm not sure what else changed along with that. 1980 4x4 models got a larger clutch disc (8.5") with flywheel and pressure plate changes to go with.
1981 2nd MAJOR rework of the LUV. Body style completely changed, interior completely changed. Gas tank now on passenger side of truck. Frame and motor are basically unchanged, with a few exceptions. Distributor is now electronic instead of points, but still fits into older motors. I believe this was the first year a diesel motor was an option.
1982-1986 Isuzu PUP continues pretty much the same as the 1981 LUV. GM switches to the S10 line, some of the 1st years of which have the same 1.8L Isuzu 4 cyl motor. The PUP doesn't really change too much up to about 85 or 86 when the 2.3L 4cyl gas motor is added. Even then the motor mounts appear to be in about the same places. 87 or so they switched to a fuel injection 2.3L and 2.6L, but still probably physically compatible. 87 was the first year in Troopers for 4x4 transfer case to be seperate from the transmission(?). Before the the tcase and transmission (including the 5Spd) should be physically compatible to 76 and newer LUV motors.
This is the article that prompted me to ask if the frames were the same,