Ok, guess its time for some 'Zu motor spec throwdown. I do have this started as sort of a writeup, but I've been waiting until I do some work on my Trooper to nail down exactly some of the "maybes". I'll try to cover the gist of it here though.
I'm leaving out the 75 and older style LUV motor, it is wildly different than everything that came after. Motor mounts on it are different from everything that came after, and so forth. If you have a 75 or older LUV, going up to 2.3 or 2.6 is more like a typical engine swap with fabbing motor mounts and etc.
G180: 1.8L Arrived in LUVs in 76, crossflow head, round intake and square exhaust ports.
G200: 1.9L Externally identical to the G180, just bored slightly bigger inside.
G160: 1.6L Heard of them in places other than the US, looks the same but obviously smaller displacement.
The heads on G-series motors appear to be basically the same. Some 1.9s do have a mechanical fuel pump bolted to the left front of the head and run off a deal on the end of the cam. There are also some rarely seen overseas G series motors with dual overhead cam, sure we'd love to have one but I think I've only ever seen one picture of one so far.
Starting with the Turbo Impulse, Isuzu started the 4xZ1 line. They are all very similar, but there are some subtle differences that have to be addressed for cross compatibility. They are based off the G-series design, but with some changes like a timing belt instead of a chain, cast aluminium valve cover, disti driven off the cam in the back of the head instead of in front on the block, and etc.
4CZ1: 2.0L came out in 85 I believe. The turbo impulse motor, fuel injected, turbo, ~140HP
4ZD1: 2.3L came out in 86 used in Troopers, Impulses, Pickups, Amigos. Up to 93 carbureted and after that fuel injected. Carb models have a mechanical fuel pump stuck in under the intake run off a lobe on the cam. Rated for 90HP in carb'd models
4ZE1: 2.6L Used in Troopers, pickups, amigos, and I think even Rodeos. Showed up in mid 87, fuel injected. Intake and exhaust ports are compatible with 2.3L, the 2.0 has smalled intake ports but it will bolt up. Rated for ~120HP
The heads for each are different. The 2.0L has smaller intake ports and the 2.3L has a smaller combustion chamber than the 2.6L They will fit together, but the compression ratio can get way too high to be usable.
On motor mounts, to my eye the 2.3L mounts in my trooper look just like 1.8L mounts from my LUV. I think that it should bolt up with at most a mix/match of mounts and brackets to the block. The 5 spd trans is longer than the LUV 4spd, so there is tranny mount work to do but its not too bad.
Up to mid 87 the 4x4 4spd and 5spds are basically identical other than adding that OD gear, so ratios stay the same just with better mileage. (My 86 trooper was getting 27-28 compared to 20 in my 4x4 LUV with a 1.8L and a few hundred pounds less to drag around.) In mid 87 when the 2.6L arrived the tranny changed a lot. It could still be bolted up with some creativity, but the cable clutch is gone in favor of a hydraulic.
There are quite a few little differences between the 2.3L and the 2.6L that make a straight swap a little complex, but it can be done. The change to the trans with the 2.6L meant a change to the rear trans adapter plate so to be "bolt up" to a 2.3L trans the plate has to be changed. This would apply to a 1.8L trans as well I think, as the 2.3L and 1.8L are actually straight bolt up compatible. The spacing is different between the two on the accessory pulleys, but if you get a loaded 2.6L you can bring it all across. The 2.3L is really easier to get into a LUV without having to collect a slew of parts to get it bolted up to the LUV gear, but the 2.6L would make some good power.
To answer a few of the questions from above:
Weber: the same carb can work, but the adapter plate is different on the 2.3L intake. The bolt pattern is not the same and the 1.8L adapter just will not fit.
Pickups came in 2WD with a 2.3L and 5spd. For the sake of ease of install and putting the weber on it, get one from 86-93 and the earlier the better.
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