HP rating on the 2.6L FI is 120, Impulse FI 2.3 is 110(Pup/Amigo FI should be similar, slightly lower perhaps), carb 2.3 is 95. The cam from the Imp 2.3 should push a carb motor up to 100ish, same cam is also used in all 2.6s from 92 on up I believe. All of the G series and 4Zx1 series motors have the same bolt pattern on the back of the motor, so it is just a matter of swapping the trans mounting plate to mount your trans of choice. 4x4 5spd is longer than the 4spd, so driveshaft work will be involved.
No one has put a 2.6 LUV together yet, but it is in the works. The only one I know of is a full frame swap from a Trooper with a 2.6L in it, but that is sort of cheating.

For the best result, I'd pick up a complete 86 for parts, that way you have everything you need, plus 4.56 diffs and power steering parts. Then get a 2.6 long block and put it all together. I've got the Trooper and once I find a good 2.6L donor I'll be set. If you want to full recipe search for 2.6L in my older posts, but taz has most of it pretty well covered.
If you want to sort out the wiring and get the fuel injection you could do it, but I figured that is just too much work for too little gain for me. I'd rather have a dead simple install with a Weber on top.
The one I'm not sure of on your list is the 4xf1 1.8L, I thought all those cars were front wheel drive. That means mounts and tranny connection would be an issue.
_________________
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
