The 2.3L (4ZD1) and 2.6L(4ZE1) share the same basic block along with the 2.0L Isuzu Impulse (4ZC1). The mounts on my 2.3L trooper look just like LUV 1.8L mounts, but it is tough to be sure without getting them out and side by side. I personally think it could be done without too much trouble. The transmission mounts for a 5spd are more likely to be a pain than the motor mounts. I think at worst you might have to mix some 1.9L and 2.6/2.3L mount parts together to come up with a solution, but my gut says a welder will not be required for motor mounts.
To get around the EFI system re-wire nightmare, you could pick up an intake manifold from a 2.3L and bolt it up to the 2.6L head. The pattern is the same. Then either run the carb from a 2.3L or get a Weber kit for it. With emissions, you are much more likely to pass with the stock carb for a 2.3L than with a Weber, but I think any swap like this will mean some headaches during the inspection. For one, almost any motor much newer than a LUV is going to need a cat unless they just don't notice the motor has been swapped.
It is all a matter of finding the right combo of 1.9L, 2.3L, and 2.6L parts to mix together and I think you can be almost bolt in other than trans mounts and driveline length. Stick with a 4spd and you could eliminate those issues too, but that overdrive gear will really help on the mileage. With 3/4 of a liter more motor you're going to be sucking more fuel as it is.
This is basically the low budget version of the swap I'd like to do. 2.6L block/head, 2.6L 5spd trans/tcase, and stuff it all into a LUV. I just want to add one little ingredient to the mix, a turbo impulse to donate intake and EFI computer/sensors. Should be good for around 150HP, a bit more with cam work and perhaps a bit bigger turbo to get enough boost for the 2.6 instead of the 2.0 the Impulse is used to.
