If your #46's on the 350 - are 1973 or 1974 models - those are really some pretty decent heads and have screw-in studs. In previous flowbench tests - they performed as well as many of the 1960's performance heads.
I forget what the chamber cc is on them.
They also have hardened seats for unleaded fuel - 1972 and older mostly will not.
But have read claims of some 71-72 heads having hardened seats. idunno
1973 and newer will have them though.
If you run under 8.5 : 1 CompRatio with hardened seats - you can use 87 octane unleaded.
Believe 9.5 : 1 CR with hardened seats - is about max for 92-93 octane unleaded.
If you get into higher CompRatio's than that - you'll need race gas/aviation gas blend(s) and lead additives and things like that. It gets expensive in a street car.
The best, highest quanity, and cheapest HorsePower comes from Cubic Inches and Camshaft selection. Higher Compression Ratio is not a big factor in street engines until way way further down the line when you're trying to milk every ounce.
Another head to consider on a 400cid is the #64 from 1970 455 HO.
80'something cc's IIRC.
The higher the CompRatio - the more you have to spend on fuel.
Heads without hardened exhaust seats - an added expense to have them installed - or added expense at every refuel for lead additive.
Things to consider.
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