Before any one here starts to port out a set of stock Chevy heads . Make sure you have a lot of extra time ! I have 7 Hours on one SB head and it's around 80% done . The heads that I am porting are the 305ci #601 55-58cc . I always hear how good they are when full ported . And how much power they make on the round and round 355 Claimer engines . Well good thing I have more time then money . I would say don't buy these 305 heads thinking you will port them easy and make Lots of power . When I am done they will work good . And this set of heads has screw in studs guide plates and S/S valves . Also a set of Z-28 LT-1 springs with HD retainers and Locks . Them old Fuelly heads never needed this much grinding