72 340 pass side manifold

65 Cuda 340 said
Aren't the ports larger on the 340 exhaust manifolds? Could be a problem sealing against the smaller ports of a 318 head. I think the 340 manifold's passages are larger, too. But I agree, in any event very little if any difference on a mild 318. Not worth swapping.

Yes, the exhaust ports are quite a bit larger. At one time I was running 1.88 intake J 340 heads on my 64 Barracuda 273. The 340 exhaust manifold casting #623 seals fine with the 920 castings on the 273 in the 66.