Not always available, BUT before I sold my '86 Jeep Comanche (2.5 AMC with Renix TBI 5 speed) I considered swapping in an automatic (904 was the option and I picked one up from a 2.8 V6 Cherokee) and I still have the TBI flexplate in my for sale pile.
Jeep also used the AW4 after '87 on the 4 cyls (all 21 spline) and another option is the Chevy S10/Blazer 700R4 off a 2.8 V6 (same bell)
The Chev 4 bangers were all SBC pattern AFAIK, so a 4L60 could be used with them, but note I have NOT checked to see if there is room under the Eagle to put them in. Just in Jeep XJs, etc (It's been done many times on the 84-86 rigs)
I guess I'm trying to say you aren't totally limited. The GM 4 cyl with GM V8 pattern can be beefed up to run say a 4.3 V6 (not saying you should)
If you have the AMC 4 cyl, 84-86 Cherokee auto is the same BUT the converter needs to be with it. There is lockup (909) and non-lockup (904).