I've built several 400 block pump gas stroker motors with different heads and different solid roller cams than yours that didn't struggle to make 600+ HP with a six pack and with RPM air gap intakes with an 850 CFM D.P. Holley carbs up
If you're wanting more power use bigger carbs like 750 CFM D.P. or maybe even 750 vacuum secondaries, I'm greedy when it comes to power, I like a lot of it devil
What are the cam specs on yours, lobe lift, lobe timing at .050 lobe lift and lobe separation angle?
is it installed straight up or advanced or retarded on the intake lobes?

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)