I have #450, 305 heads that have 202's and screw in studs and guideplates, new springs, clips, retainers, and were ball milled to open them up behind the valves, and are 58cc.
On a 406 with 287 duration cam, for 2 1/2 years of every day driving, runs strong, and runs great, untouched for 2 1/2 yrs.
It cost me less then I could get Vortec heads to the same point.

You would have to notch your block to put them on a 305 again.

Pat