fwiw: We had Wilson port the indy single 4 intake and picked up over 35 hp and thats with a 4150 flange.
Its pretty amazing how much flow restriction/turbulence is in the intake's.

Just a thought.

We were looking for 6.41 this year at 3345 lbs and got to 6.37 .
Night we pulled the .37 i still had another carb formula in my pocket but ran out of time, pretty sure we could have pulled a .35- but i reckon i'm bench racing now- grin.