With the 3.2L and a 5 speed, you're definately looking at pretty much a full drivetrain swap short of the axles. The 3.2 is an Isuzu-specific bolt pattern that doesn't match any of the GM motors.

With that said, if you're going to be going that all out on the swap, you may as well decide which engine you want to work with, or can get your hands on, and then find the parts you're going to need (transmission, t-case, bellhousing, etc) and go from there. For power, the 4.3 is a good option, and will fit with less of the longitudinal squeeze being found by those doing V8 swaps.

When people talk most commonly about doing a swap, it's the 3.4 Troopersphere was talking about in place of either the 2.8 in the Troopers, or the 3.1 in the early first gen Rodeos. Since this is not what you're looking at in any way, you may as well just decide what you're going to use. In some ways, it's potentially simpler to work within the GM family, as Isuzu pulled some parts and connectors from the GM parts bins, and there may be some plug-up parts, but it would be pure chance if it happened.

If you want the 4.3, look for S-trucks, Astros, Blazers, or even 1/2 ton full-sizes. The 4x4 variants of the trucks will get you the transfer case you need. You'll probably have to have driveshafts custom fabbed for the specific application, and motor mounts are going to be a custom job as well.

Make your plans ahead of time, and you'll save yourself some headaches. Keep us informed of the progress, and let us see what you're up to!

James