He's probably got enough of a ridge in his cylinders that they'd be rough on rings with a higher CR piston.

I agree, milling heads is more trouble that it's worth. Save the money towards your engine rebuild later on down the road.

Also your stock heads were more like 90cc with a .020 gasket. The source heads have been cc'd by others to be more like 86cc. 86cc with a .039 gasket will give you the same CR as stock 90cc with ah .020 gasket. No loss, no gain there. I've got a 76 440 with stock smogger pistons, I put in a new set of rings, bolted on a set of 440source heads, headers, lunati voodoo 60303 cam and (temporarily) a stock intake and thermoquad. It runs well and puts out good torq considering I threw it together out of parts I had laying around.