After reading everything you wrote below, I think the cam listed would do fine with the 3.23 and stock stall converter and tire size. The best mix of exhaust manifolds would be 1 340 exhaust manifold and 1 early Magnum exhaust manifold. You'll have to stand by for the part number IF I can find it, but it comes from the first few years of the Magnum exhaust manifolds mostly found in Dakota's and Ram's. The outlet size is the biggest @ 2-1/4 inch.
I wouldn't go to much larger for a cam myself with the running gear you have now.
Port the 302 heads? OR go to Magnum heads? Often a catch 22 since porting the head is going to be more expensive than getting new Magnum heads, but the rest of the conversion parts needed will just about balance an out to equal price tag.
The only big bennifit in the Magnum head use is the 1.6 ratio and the better ports as cast or ported over the "LA" head, but that's more money over the intail conversion. Catch 22 again.
Your call.
