I ran a 296 degree 557 lift Purpleshaft cam in a 440 with 906 heads and TRW 6-pack pistons...twenty years ago! As I recall, I put one head on the block w/o a head gasket and some clay on the piston, set the valves in that cylinder to spec and rolled it over. It must have cleared with room to spare, because the engine ran great and the car was very consistent.