1963 NASCAR International Rule Book Specifications NASCAR Grand National Championship Circuit Section 20-9 -- Bore and Stroke

a. Engine size (displacement) increase as a result of permissible overboring, measured at the base of the cylinder, is .010 for all eligible models, providing the total displacement does not exceed 428 cubic inches. Stroke must conform to AMA specifications.

b. Cylinder blocks must be production with standard measurements in all respects with the exception of the permissible overbore. No interior or exterior reinforcements permitted.