1971 NASCAR International Stock Car Racing Rule Book NASCAR Grand National Championship Division Section 20-14 -- Frames

a. Frames may be reinforced and altered in the interest of safety and to permit the use of 9 1/2 inch wheels, exhaust headers and shock absorbers. But the wheelbase must remain the same as manufactured as referenced by measurements from the front door jamb post to the front axle. Unit construction cars must maintain their original body dimensions. Alterations will be permitted in interest of safety. Unit construction cars must maintain minimum ground clearance. Tire wheel base must remain the same as manufactured as referenced by measurements from the front door jamb post to the front axle.

b. Frame modifications are permitted for tire clearance if similar to original equipment in design, appearance and dimensions. Modifications must be reported to NASCAR Chief Technical Inspector and frame must be approved for safety and workmanship. Any frame rejected by the NASCAR inspector for being unsafe or showing poor workmanship will not be approved until necessary corrections have been made. A piece of channel iron, minimum 4 inches by 1/4 inch, must be installed between the bumper and the rear cross member of the frame by welding to frame rails on each side and bolted with a minimum of four bolts not less than 1/2 inch diameter, evenly spaced between the frame rails.