Manifolds. Everything external is factory, and leaving it that way.Sounds like the Melling cam the right one. I might have missed it but are you using long tube headers?
Holley has a 500 cfm 2 bbl. I honk 500 cfm + longtubes/ 2.5” pipes all controlled by a 340 cam would make a great 360 cu. in. air pump.
A few minor inside mods I toy with