Rob,
Weren't they protested because of the use of the controversial
Carter #3447 AFB Carburetor, which was permitted by the NHRA.
The 600 CFM rated unit, that was used on the 1963 '426 Max-Wedge' engine.
The #3447 had a 1 7/16" Primary and 1 11/16" Secondary, and the
273 Cast Iron Intake required the 'secondary' bore hole to be opened up.
That 600 CFM AFB did make a big difference over the 'stock' 500 CFM AFB.