1968 383 piston replacement

I would replace with somethign with a valve relief. With stock heads, the gaskets available, and pistons available you will struggle to get past 9:0 without having some blueprinting work done on the block and heads. But that being said - if basically "stock with a little cam" is your goal - I would say don't worry about it. Use the KB-162s, use the MP thinner head gaskets, and let the other numbers fall where they may. Assuming the machining is good and the cam choice is good - it will make at least what it made new, and depending on the valve job and parts used, probably more.