1963 NASCAR International Rule Book Specifications NASCAR Grand National Championship Circuit Section 20-23 -- Rear Axle

a. Rear axle ring and pinion may be any gear ratio listed in manufacturer's catalog, and must be available for delivery through regular dealer channels within 10 days. NASCAR reserves right to limit ratio.

b. Manufacturer's cataloged heavy axled rears may be used provided no alterations are made to body, sheet metal, frame or suspension other than those permitted in special bulletins. No quick change, limited slip, or locked rears permitted.

To clarify this specification; all Ford products shall be classified as in the same line, as well as General Motors, Chrysler Corporation and Studebaker-Packard. Example: Dodge differential in a Chrysler 300E. Wheelbase and tread must measure the same as those listed for the model to be raced.

c. Full floating rear axle compulsory, but must not alter tread width or general appearance.

d. Differential oil coolers, approved by NASCAR, permitted.