Ive got a set of stock 243's i got for a steal and want to use them. My question is how much can i mill them and still use stock length pushrods? Just trying to get a bump in compression and extra power. Nothing crazy. What would the compression be as well?

The car is a daily driver. I will be using stock gaskets as well.

 

unmilled they will raise your comp from 10.1 to 10.45, some have milled them
as much as .030-.035 but that will affect your piston to valve clearance
particularly if you have a larger aftermarket cam. Also 243 heads off ls6
engines have lightweight hollow stem valves which are 0.6mm or 0.0236 "
inches longer and can affect your pushrod length. Know what you have
and measure things to get it right. (sweat the details)