I'd be careful about milling the heads if you plan on doing a rebuild on the short block later and gonna do the zero decked, 0.040" gasket Quench thing because the stock 302's 59cc chambers gonna give 10:1 so any milling will give too much CR later. Problem is the stock CR right now is low to mid 8's which limits cam selection need 9:1+ to be able to use decent cams 265-280 range. Pistons are the only proper way to get CR out of a 318 or mill the crap out the heads for now and upgrade to better heads when do full build and sell your temp heads after to someone looking to hop up a stock short block but even without milling I would install bigger valves and porting the heads thinest gasket you can get and high lift 262 cam and headers will get you close to 320hp more CR and a bigger cam 350hp.