We used to build a bunch of low CR(8.5:1)350 Chevy oval track motors.
They had to use heads with 1.72” intake valves, stock 2bbl intakes, stock ex manifolds(and not the good ones), and under .500” lift hyd cams with stock rockers.
A pretty good one would make about 280hp.

I tried a set of 1-5/8” headers on one once...... just to see.
It picked up 42hp.