The sportsman heads can be nicely ported. Local here used those heads for quite a few years before upgrading to vic jrs. The car (67 Camaro) dipped into the 10s a few years ago with a 355.He then build a replacement 383 with victor heads.
The sportmans when ported flowed 265 CFM.
The headers you have should have a 7 bolt flange if they are 1 7/8 tubes. Those are big tubes...If they are hooker headers,make sure you buy the hooker pattern for the inside gasket if you replace gaskets