i have a stock 440 block standard bore and stroke. will a .590 purpleshaft cam open the valves too far and hit the piston? or do i need pistons with eyebrows?

You will need pistons withs some compression to make that cam work good and yes I feel that you will need reliefs.

It would depend on how far in the hole you are & with stock pistons if you are far enough down to be safe as mentioned you wont have enough CR to make it work.

RR got it right. If the pistons are down far enough that you don't have valve interference, the compression ratio is so low that the cam won't work.

BUT, the cam is too big because the 440 stock pistons and rods aren't made for high rpm where the cam starts making power.

So what do you really intend to do with the car and what car is it?

R.