Mr. Cavebull.. Actually, your math may not be off.. I just found out what MA 1214 means.. MA stands for 3:90 gear ratio and the 1214 supposedly stand for the month and day it was built..
So that would knock your calculations off slightly if you were thinking this was a 4:10.. Now my rear end guy didn't actually open up the pumpkin to look inside but he did mark the tires and roll it to count the rotations.. He came up with the 4:10 which is pretty close.. But I am more inclined to believe it is a 3:90 based on your number crunching and the RPM's I am currently getting at 60 mph.. and the fact that it has "MA" stamped on it.. Still, the 3:90 or 4:10 or whatever, is still way to low for my blood.. I'd like to try a 3:08 if I could swap out my 10 bolt for a 12.. It seems only the 12 bolts had the 3:08's in them.. I'm working on trying to find the answers.. One thing for sure I have noticed about rear end information, it seems to be an elusive thing to many and not an exact science.. Definitely everyone has opinions stretching the spectrum.. I'm actually quite amazed it is so difficult to get strait answers.. Perhaps part of it is that everyone has different needs and expectations and experiences.. So my challenge is to sift through and try to make an educated guess on the poison that best suits me.
I ran into a guy that said he was the go to guy for any and all parts that these Chevy/GMC trucks needed in the early 80's.. He said people ordered through him on the eastern seaboard and that there was another company out on the west coast called Goldcoast or something to that nature.. And that everyone went through them on the western seaboard.. Anyway, he said that he owned dozens of these old chevys with all the different engines from 60-66.. He is the one that first told me that all those rear ends swapped from 60-72.. Then he showed me pictures of a 1970 rear end he put in a 63 c10..
I'm still doing homework and I really appreciate this site.. all those links very helpful..
