Learn all about Muncies here:
http://www.5speeds.com/muncie2.htm
Go here to see comparison of gear angle on M21 and M22:
http://www.5speeds.com/muncie3.htm
Here is page 1 if you want to start there:
http://www.5speeds.com/muncie.htm
Sounds like you are looking at a Super T10, and not just a T10. Big difference. This is a good example of buyer beware on Craigslist IMO. The Super T10 is a really stout transmission with lots of aftermarket support.