milling heads for comp ratio increase

For a nice 273, you have all you need. The 273’s with the open chambered heads usually had pistons that were .020 higher in the bore. That pretty much puts them at 0 deck height. It typically takes a .040 cut to get to the NHRA minimum chamber cc’s. Usually machine shops charge the same for milling up to .020 of an inch. Then I’d cut the intake side of the head .019. If your shop can’t figure how to cut the intake side of the head, find another shop. If your valves and pistons seal, That is good enough. Use Felpro head gaskets and be done. You have the carb, intake, and cam. Just use good valvesprings, 340, and Viton valve seals while your in there. Add a windage tray and a double roller timing chain. Tune it, tune, tune it.