You get to a point of diminishing returns on inches if you have a small head. Liking drinking in air through a straw.
No matter the size motor, its going to take W8-W9 or perhaps the new Victor heads to make 700 on pump gas
NHRA pro stock motors are 500 inches. They are only roughly 3 tenths quicker than 900 inch mountain motor pro stocks.
So cubes wont solve many of your issues. Just move the powerband down
