SBC rockers will not work correctly on the Chevy inline 6 cylinder head. The geometry is completely wrong for this head. The BBC rocker is the only correct substitution for it(Chevy-wise) but it has less ratio at 1.7 than the 6 cylinder has with a 1.75, but has the correct geometry. Roller rockers for the BBC are cheaper than the 6 cylinder also if your price shopping.
