Please help.

[10secopcar]

I am new to the carburated world. I have a 71 swb with a 402 I think. it is a big block but I have no idea where to look for casting numbers, block or head. The tag on driver fender says part number 3994016, is this the block casting number? I did however look up the exhaust manifold numbers and they are apparently from a 73 454 police edition motor. Are these the ramhorn manifolds? It is bagged and i wanna put longtube 1"3/4 headers on it. But I am not sure about the oval port or round port part and not sure if they will hang below the frame. Sry for all the questions just new to this era of truck and don't know alot about them.