That other motor would have certainly made for an interesting "science experiment".

Swap out a component at a time until you find what's holding it back.

Was there really one thing that was a major contributor, or was it really just a few things that each played a part in the less than expected/desired results?

I will say this, from my perspective....... I don't see anything glaringly wrong with it "on paper", and would have also been looking for better results myself.

This is slightly off topic, but this thread made me think of it again......
I'm really surprised no head company, even someone like Pro Comp has offered up a new aluminum W2 head.
All the support products already exist..... Intakes, rockers, headers.
Just cast the long valve W2's in aluminum. Use 11/32 bronze guides, come up with a more modern closed chamber........ I would think they would sell pretty well.
They're a known quantity........ They work.

Anyway....... That's just a thought from a BB guy.