Does anyone know where I can find information on what kind of paint I should use on the frame, rear, ect...ie.. flat, semi.. for my 1971 Chevelle?

I believe what you need is a flat, but I'm not sure of the true correct particulars.

If I were doing this, I'd use POR-15 Chassis Coat Black. You could get it here:
http://www.por15.com/

If you're looking for the ultra-correct answer you might try this post in Restoration Corner, or hang around here and wait for the experts - they'll be along...

Hope this helps.