the square port heads flow a lot and can make over 700 hp. Are they closed or open chamber? after you flow test the heads you pick a cam that fits the flow chart. Oval port heads can support over 500 hp if ported.2.19 intake valves are also a good choice.
my 1980 z-28 with LS-5 454 took me into the high 11s. I doubt it was 375 rwhp. I used GM oval port heads with 2.19/1.88 a Z-55 isky cam,Jr oval port manifold,830 annular double pump holley,flat top pistons, open headers.car weighed 3915 when I bought it and managed to get a little over 300 pounds out of it.