do I have a Gen IV big block?

[longbedrick]

Assuming my 1973 GMC 454 is all stock, is there a good chance that I have a Gen IV 454 motor? Seems like there is a whole lot of variation. 2 bolt, 4 bolt. oval port, square port, peanut port. oval large, oval small, oval standard. rectangular head. standard head. open chamber, closed chamber heads. can all this be cleared up by the casting #'s? I'm just trying to buy an intake manifold, and I'm getting all these promts at Jegs and Summit