1968GMC
I dont remmeber exactly but I think it was from 2100-2400. If it were me and I had the $$$$ I would get my 3.73 back and put in a 700r4. But since I dont have the $$ the 308 will do for now. Also this is a handly little tool for the rpms.
http://www.angelfire.com/fl/procrastination/rear.html