But... dual plane cylinder-to-cylinder (and bank-to-bank) distribution changes more than other designs:
1. with RPM
2. with engine vacuum

Working to correct runners WOT at peak may give a big flat spot somewhere, fuel drop-out, black & white plugs.

harder than it looks.

I heard Brzezinski did good work on dual plane iron manifolds: https://tinyurl.com/y7xvcsas