[Walt Fricke]

Crash

The early SC heads are the big intake port heads. They require the larger intake manifolds.

You can open up the ports on the later US heads to match the early/Euro head ports.

But you wouldn't want to try to open up the later, narrower, manifold runners. You could probably do that down at the port flange, but that won't do any good with the air flow out of the air box, where everything needs to be larger as it was on the early SC and the Euros.

If you port matched the smaller port runners to your larger port heads, that might be part of this puzzle.

Perhaps you just misspoke? And you have the larger intake ports and the proper runners to go with them?