Originally Posted by cobalt327
Interesting page on the Buick transmissions, like used in your '64 Riv: Transmission Swaps & Modifications
. Seems there were ST400's used in '64 Rivieras (guy says he drove one for 13 years, even describes the peculiar shifting of the ST400). Maybe Buick used both, but the TH400 wasn't mentioned.
LOL, I just PMed Moose with a link to that site, it's my brothers site and is a nationally known Buick Nailhead expert.