Concur.
A good plan would be something like this:
Look for an S-series (S-10/S-15) with the THM700R4 and NP231C transfer case, and the 3.1L or 3.4L engine. Grab the entire drivetrain - including fuel injection and control electronics.
If you have trouble with the S-series "entire drivetrain" approach, you can expand your engine search to the F-body (Camaro/Firebird) for the engine, and you can even slide under FWD donors - Goodwrench Service Replacement (GSR) engine blocks came with starter motor mounting pads on both sides of the thing, and if a GSR engine has been installed it may be identified easily by the unused starter motor mounting pad on the back side of the engine (as mounted.) Grab the control electronics from there as well, and get the FI (which is an improvement over the Weber.)
If you do go with the THM700R4/NP231C route, be sure to get a transmission made after the 1987 model year - early THM700R4 transmissions had a fatal flaw (I don't recall the nature of the flaw offhand) that is essentially irreparable and required total replacement of the unit.
You will have to fab up some variety of mount from the existing crossmember, but using the THM700R4 (or the later 4L60 - avoid the electronically-controlled 4L60-E, however) allows you to pick up an overdrive gear that the A904 used as OEM behind the 2.8L V6 (1984-1986XJ) lacks. This will reflect in your wallet!
It is fairly likely that you will also need to get new driveshafts made to accommodate the THM700R4/4L60 + NP231C swap, but if you're going to drive the thing extensively, it will likely be worth it.
(Note that, if you can't find an S-series with the desired combination, you can also find the THM700R4/4L60 as a 4WD version in the Astro/Safari van with the proper bellhousing. Also, I believe that the bellhousing of the thing is removable, so you can find a 4WD version of the transmission + transfer case in K-series trucks and Suburbans - most likely K-10, but some K-20 - and get a RWD V6-60 bellhousing from an F-body or an S-series. It's a Frankensteinian approach, but it's doable. It's quite a lot of work to convert a RWD transmission to 4WD, and note that FWD and RWD/AWD/4WD have starter motor mounting on opposite sides of the block.)
It should be noted that engine control electronics tend to be more adaptable than transmission control electronics - this is why you can swap in EFI-controlled 3.1/3.4L engines, but you'd prefer to avoid the 4L60-E transmission (although the THM700R4 and 4L60 are both internally hydraulically controlled, and therefore don't require control electronics. The A904 is also internally hydraulically controlled, so you don't have to worry about it.)
Another option is to get the SBC mounting cradle from Advance Adapters. This will allow mounting of any Small Block Chevrolet V8 engine - and, with a bit of fabrication, the transmission and transfer case should go in neatly as well. This should be easier for you to find - K-5 Blazer, K-10/K-20 pickup/Suburban, possibley K-30 pickup, and there are quite a few G-series Vans made 4WD as well. Note that the one-ton trucks/vans tend to have heavy-duty three-speed transmissions, which is why I lean more toward the K-10/20 versions instead (by the time they got overdrive in the one-tons, they were also electronically-controlled, typically the 4L80-E.) The 4.3L V6 also becomes a swap possibility, as it is based upon the Small Block Chevrolet V8 engine (and shares bellhousing pattern. I believe the 4.3L also saw use in the F-body, Astro/Safari van, and S-series pickup/SUV - I'd have to check my notes.)
So you see, while going to the 3.1L/3.4L is a valid drop-in swap (if you want to keep the carburetted version, you should be able to upsize the Weber slightly and put that on the 3.1L/3.4L as well,) there are quite a few options for you, depending on what you really want to accomplish with your swap. The choice is yours...:lecture::lecture::lecture:
