Quote:
Originally Posted by unruhjonny
where did you glean either of those numbers from?
I'd like to help, but am confused by the question.
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The numbers the OP gave are out of an early to mid 70's dated Pontiac Master Parts book. That might have worked at the dealer 4 plus decades ago. Such an over the counter complete new Muncie 4sod for such a '70 model would have CTC- (a single digit number) stamped in very small digits into two spots on a "661" case.
Looking for a correct '70 GP 455 application Muncie 4spd, it would indeed be the close ratio/ M21 with correct speedo drive gear for 3.31 & 3.55 rear gear. Same two letter coded M21 was avail behind a '70 455 GTO. Originally, a very early '70 model application would have a "660" casting Muncie case. Later in the Fall of '69, Muncie 4speeds were built with the first "661" casting cases. Both casting cases were combined with the same small output tailshaft housing for thus applucation. Not extremely hard to come up with either '70 casting number M21, it's coming up with a correct dated one that will be a challenge if one is very serous about restoration.