How much can valve head OD be cut?

With aluminum heads I doubt you can make too much cylinder pressure on a 273 no matter how hard you try, lol.

53+8.8+0deck and 5cc eyebrows totals 66.8 and will give a stock-bore 273, an Scr of a measly 9.416. By the time you put a small cam in it (say 62* Ica) she'll be down another two points to 7.6Dcr (at say 900ft elevation), which being about a full point and a half lower than decent to get your monies worth of performance from aluminum heads. At 7.6Dcr the cylinder pressure is predicted to be 148psi. In my experience, the aluminums work great at over 185psi and mine still burns 87E10 at full timing at .034Q

Some guys here on FABO claim to be running their strokers at over 200psi on pump-gas, and I have no reason to doubt that. I have seen 200 on my gauge at one time, and it ran very very very nice.