Purpleshaft .484 Cam in a 273?

If you are putting in 2 BBL, lower compression pistons and the later open chamber heads, the static CR is gonna start low and the dynamic CR is gonna drop pretty badly with this cam. Low end grunt will not be good at all.... IMHO, to make up for this partially, mill the heads to get the chambers down in the low 60's or high 50's cc range and use the higher CR pistons. Advance the cam some as suggested.

BTW, how would you be using this engine? A lot of how you think it turns out will be in how you use it, and a lot of subjective judgments on how you like things to run; high revs will be the name of the game here.... which goes with the gearing comments.

IMHO again, a turbo would be GREAT here but this is totally the wrong type of cam.... waaaay too much overlap is the main problem. If you do consider this, then the lower compression is ideal; stay down in the 8:1 Static CR range, and limit boost to around 10 psi tops. Since finding forged pistons is not gonna happen and you will have cast pistons, then the pressure needs to be limited for reliability. Turbo selection will become the key to the low end response; in that case, less is more.