WIW X-Heads

My issue with used heads is the unknown. It's difficult to tell if they have been milled.
During a 40 year lifespan they may have been milled .03 only once or .02 three times.
Milling the heads screws with pushrod to rocker geometry. Then you'll need shims under the rocker shafts. Fun aint it ?
Good luck with whatever you choose