The problem is, until you match the chamber depths and polish the roof until its flat, you cant get a tight quench. Tight for a 4.03 bore with stock pistosn is .030". The casting contours are close to that tall. I did one engine with open chambers looking for quench. I won't do another. If it was me, and seeing as 1. it's for a '65 and 2. you may upgrade the rockers anyway... I'd use a larger solid flat tappet and drop that static a little. Just my thoughts, as always, it's your dime/build.