Just a suggestion -
My LS5 '70 had an original LS5 motor in it, built in the early '80's - I detuned it back to nearly stock specs, using the original low profile cast iron intake, 7040204 Rochester (which flows about 800 cfm), 10.25:1 pistons, Comp Cams hydraulic, stock lower end and LS5 heads, SS valves, headers. Car is a 400 Turbo, had 4.56:1 Eaton posi (originally 3.31). Factory air -
Even with the heavier Chevelle, it would do a complete doughnut if you allowed it to - not dynoed, but horsepower and torque unlike anything I've ever owned. Yet - idled great, instant response, but very harsh shift because of a doofus shift kit previously installed by the prior owner.
Don't discount Rochesters as a performance carb - they flow great, good economy if you can get used to the secondary moan when you put your foot in it. Watch your cam profile to allow for power brakes and the air, also. Select your compression for pump gas unless you want to spend a fortune on race gas or octane boosters for a cruise night -
Just my opinion -