I've got a 1969 383 engine from out of a 1/2 ton pickup. It was a 2BBL with a 3 speed manual behind it. The block pad by the alt. has a lone letter "R" on it. I was wondering what this means. Also I was tickled to find 906 heads on it!!!!!!! It also has a steel crank.... pretty sure it got that because it was a stick shift. Anybody?