Stockish 340 upgrades, cam needed

Should I get the pistons milled then to bring the compression down.

I think you would be better off with .053" head gasket and .015 piston pop up(.038 Quench)
then a 0 deck piston and a .053 head gasket aka .053 quench = NO Quench!

Also .015" is not going to change you compression enough to worry about it. but will destroy Your quench!