I'm gonna say
to the forum! I'm running a TH400 in my '69. They were introduced by GM in '65 model cars, and were installed until they were replaced by the 700R4's, which were superceded by the 4L60E. So, there's a lot of TH400's out there.
One question: Why a TH400? I also had another '69 that had a TH350, behind a 350 that was built and would chirp the tires on the 1-2 shift, every time. The 350 has a little shorter first gear and lots of people prefer it to the 400.
So, what are your plans and how does the 400 figure to be the transmission of your choosing?