It would be easier to find a 455 than a 389 or 421. Start checking the local
yards. Most have parts locating services and can set something up from a
different area. Pontiac used three speeds in some cars, most use the same
bell housing as the four speed. Almost any GM style four speed will work.
You may be able to get a new one from Richmond.
http://www.richmondgear.com/01transmissions.html Close to stock would be the
T-10 series. Muncie's didn't come out until after 64.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.