John,
If I read your post correctly, it sounds like you have a’53 “SM420” currently installed. Yes/No/Maybe so??!
Lots of SM420’s to be had if you do some web searching.
It may be less money to pickup a complete trans for parts.
I am currently away from my resource books, but would be glad to look up specific part info and post that here tomorrow if you like.
Others will be along to offer more help as they can.
Have a great evening!
Dan
