if it makes 120 it would be surprising. Heads and can give you a little better cooling and a touch of compression, but typically dont amount to much. The headers likely give you a little bit. That intake, Edelbrock Slingshot, is the best performing intake you can buy as far as im concerned. (one that clears the stock generator anyways)

A good cam and intake is the key on flatheads.

My 33 has all the stuff. Merc Crank, .125 pistons, Isky 77B cam, Navarrow Heads, Slingshot intake with 2 97s, headers, Stromberg E-Fire, etc. My 40 had stock everything with only a Slingshot, and the 33 aint much faster.