Conversion >> TH400
The Turbo 400 is a 3 speed automatic. People will argue all day if
the TH400 or the TH350 is stronger, who knows. What everyone does
agree on is the TH350 is shorter and doesn't use up as much horse
power. Short is import for most Jeeps, but you might consider a TH400
if you happen to have one or you think they are stronger.
Jeep versions of the TH400 might not be the best to work with for a
couple reasons. The version bolted to the Quadratrac transfer case
uses a unique bolt pattern and spline count that makes in not useful
for other applications. The version bolted to the Dana 20 has an
adapter from the factory that has a reputation for breaking.
It might be possible to take an AMC case TH400 and use a Chevy 4wd
output shaft and adapter to get a low buck conversion. I haven't heard
of anyone trying it though.
The TH400 has been used in GM cars and trucks and Jeep trucks. The
following articles cover some things to look for to find the TH400 you
Jeep TH400: Jeep used the TH400 starting in the 60s and up to and
GM TH400: Chevy used the Powerglide in the 50s and 60s.