All for .370 lift and under ........

I remember trying out a 318's 2 brl carter on my built up 227/6....leeeeeeean..

Tried a Rochester 2g off a 69 307... riiiiiiiiich.

Got me a holley 350 cfm.... purrrfect.. right out of the box with the exception of the pv too low a rating.

An idea ,diff motor, but still an idea on calibration.
My slant head flowed about 190cfm
318 heads stock are like 175-180cfm 'before the intake goes on'..then its worse.
I've taken a ported 302 and bolted a iron 4 brl intake to it...148 ish cfm with clay on the carb flange.

That's where I would start digging for power, the intake manifold.

Best of luck