Need help tuning a six pack

I guess I'd want to see pics of his setup
before I'd hazard a guess.
Stock or aftermarket setup?
Carb numbers would be a start.
Manifold vac at idle & rpm and altitude.

That's assuming all the rest of engine/ignition is sorted.
If its that jackedup, I'd install a dual plane and single carb
just to see if its not something else not right before
I would place blame on the sixpac.
He could block off the two outboard carbs
with plates and see what he has.
If it won't run right on a 2bbl at least hes narrowed
it down to one carb or something else.