Its a rule that people have complained about for years. If you want to run a certain class you have to build a car to fit. Just like competing in NHRA, X275, No Prep Kings. They all have rules. The line has to get drawn somewhere. I've heard complaints of different body style, small blocks, trans brakes, data loggers, rack and pinion, aero scoops should be allowed. The bottom line is the answer has been no. I don't see it changing. So often classes get watered down. This class has stayed true to it's origin. There is a rules committee. They sit down every year and discuss if there will be any changes. They poll the racers themselves and then decide. This year single Holley's are allowed on Mopar's. They also outlawed digital dashes. Last year there was a big push for rack and pinion. Some complained that standard steering was unsafe. That was turned down as well. You correct it is an index class (not bracket and yes there is a difference. I run both). This class was conceived to showcase "factory" Super Stock package cars. Max Wedge, race Hemi, Thunderbolts, swiss cheese Pontiac's, 409 Chevy's, lite weight Galaxies, ETC. The last package cars sold were 69 AMX. Granted there are a few in the mix that weren't there at the beginning. Old's, Buick's, Fairlane's. But there vintage fits. And those cars were being raced new during the time period. The engines have stayed true as type. No Hemi's in pre 64, no 396/427 in pre 65 , no Lima series in any Ford.
Doug