Another thought for you since you require an automatic;
The GM TH425 auto transaxle from the Cadillac Eldorado / Buick Riviera / Olds Toronado has the right configuration for what you want to do... They are extremely strong transmissions but are driven via a Chain similar to a 4wd transfer case (although very silent).
These are not computerized and you can find bellhousing adapters out there if you look hard enough..
Here's a guy that did one in a Manta kit-car;
Rick's Manta Montage