Hope you ain't going to just get, and bolt on? Besides having them machined for 1/2" Head bolts $50, have a reputable Olds builder go through them, like Knowlton Thunderheads. Install bronze guides, Teflon valve seals (DO NOT USE CHEVY ONES), get a competition valve job, blend bowls, port/polish the ports and combustion chambers, mill heads 0.030", Fill heat riser passages with zink alloy ZA12, Braze the center divider on the Exhaust Port, and surface milled. Purchase new 2.120"/1.710" stainless valves, and get them undercut, and new springs/retainers for your cam, and use .027" cometics head gaskets, also run BB intake gaskets
Get them C heads to flow.
226/128 (stock) to 265/175 at .500 lift