I had a '64 Jeep Wagoneer ...
[more about Jeep than you ever wanted to know]
Yep .... starting in the 60's [CJ 5, 6, 7 and Commando era]
Jeep made a 4 cyl ... old WW II era flat head
bought all the tooling for the 225 Buick V6 in 1966 [the factory discovered a dealership in the Mid west replacing the flat head 4 cly with the 225 and how popular it was] - in 66 GM was getting out of the V6 business, so Kaiser / Jeep bought everything .... smartest move I have ever heard of a manufacturing doing - if you got an AUTO is was a Th 400 [although Kaiser did use a Borg Warner Cast Iron auto in the early days] Ford Style Starter, Brigs and Straton keys
in 1972 the V6 tooling was sold BACK to GM [how is that for irony] and AMC I6s and V8s being the standard in CJ's and Commandos [which only lasted to through the 73 model yr]
Wagoneer's and J Series PU had a ;
232 / 258 I6 AMC Motor
327 AMC Motor
350 Buick
in 1972 when Jeep was acquired by AMC - Wagons and PUs got AMC V8s but kept the TH 400 Auto Trans [used various T-XX manual Trans] in the mid 72 model yr AMC started using Torqueflite 904's and buy the early 80s was using the 727 in the Wagons and PUs
even after acquired by Chrysler in 84? the AMC 360 carried on in the 'Grand Wagoneer's until the end - with the smaller 'XJ' Cherokees getting the 4.0 I6
the TH 400s were the Buick, Olds, Pontiac bell housing not the more standard Chevy [square top version] there was also a 1 inch adapter for the fitting TH 400 to the AMC Bolt Pattern
[I could break it down to Transfer Cases and Axles - but I doubt you want to know that much]