I’d say the basic combo would pick up power with the 337.
How much of a gain there would be……..only one way to know for sure.

And…….the port mismatch is probably not going to help matters.
But, it may not be the kiss of death either.
Again, you’d have to try it to know.

I’ve tested BBC rectangle port manifolds on oval port heads(which is a huge mismatch) that picked up power over their oval port counterparts.

If the manifold is priced friendly enough, just try it.
If it doesn’t do what you want……. Flip it.