When it HITS!!!! No,too many variables,piston,flycut,rod length(stock you said)head milled,cylinder milled,etc.All you named be OK,125/75 and 315 might be more higher rpm power,295 or 125/65 be my choices,not familar much with the'63's.Most time .080-.100" piston to valve be fine,can get closer,but riskier!
. Now if you want to ride with more power esp up top,125/75 or 315 be great! Bill