So I'm going to EFI, will be running 540cid F1c Procharger and a 370ish intake cfm heads, boost will be low 6 to no more than 10lbs. I'm driving myself crazy over the intake I've decided to use the SPX as I have it already, it's a 4150 flange, but with the larger Blowers and big cid 4500 flange desired, no real big deal as I can open the plenum exposing the runner walls which would then be knifedged etc . Or would leaving it somewhat 4150 size maybe open it 1/4in around and do the same to the 4500/4150 adapter and put a "neck" in the plenum with the larger 4500 opening on top blending down into a slightly larger 4150 opening of the intake? Would that promote velocity? In my mind it would, or would it be a restriction?