Crankshaft Identification

I have a 5.0 crankshaft and I'm trying to identify it by casting number. Here is the problem, there are only a couple of numbers on the crank and not a full casting number. The only numbers I could find M-12 A. There is also a 13 and 14 stamped on two of the journals. Any ideas???? I can't find anything on the web.

Thanks!

My '90 crank has it but this one doesn't.
I did find this chart so I am looking through it now:
http://raceabilene.com/kelly/hotrod/engine.html