I have a set of C9OE heads on my car but I did them myself as I work in a machine shop. I put in 1.94-1.60 stainless steel Manley raceflo valves ,hardened ex seat inserts,solid bronze valve guides,dual springs,studs and guideplates. Plus I ported and polished and C.C.'ed them. I spent 14 hours on the exhaust ports alone. Then I did all of the machining like cutting spring pockets,milling,counterboring for the ex seat inserts, drilling and reaming the valveguide bores to accept solid bronze guides,pulling rocker studs and machining + tapping the pedalstals for the studs and guide plates.cutting the valveseats,Etc. It can really add up. I go 12.50's with these heads at 108-109 m.p.h. N/A. That is why I mean it is not cost effective to do these heads right unless you do them yourself. There are guys going alot faster with these heads also. But for what you'll have in to them you could have aluminum heads and alot less weight up front.