If it wasn't in added weight, it was in "factored" power ratings. If it appeared an engine was over-rated in their factory horsepower ratings, they might make a 383/325 into 383/300 for class definition purposes. Or in the case of the 340/275, I believe it became 340/290? In some cases, the weights attached to different models of the same car could be different AND provide a class advantage if you played everything correctly!
For example, a local 2nd Gen hot rodder/mechanic discovered that a '80 Camaro Berlinetta had a "better" weight than a Z/28 did. So he built a '80 Berlinetta with a 455 Buick motor and became quite competitive in the chosen class. All it took was a pair of "Berlinetta" name plates!
Sometimes, I think it's the psychology of being "under-dogged" by these regulations that makes "losers" before the race begins? IF you do feel "under-dogged", then doing things to a higher degree of execution is needed. Whether it's in tuning the motor, a better tire choice, a little more gear, or a Chrysler-spec drag racing wheel alignment. BUT when you hit that magic combination, it's all better!
For NHRA, NASCAR, et al, it's all about "the show" and getting people to pay to see it. If some might complain about a rule change or whatever, that just fuels the fire and makes things better. It's always been quite obvious that when Plymouths/Dodges regularly win, it fires up the Mopar people and bores the BowTie/BlueOval people (because THEIR favorite brands aren't winning), by observation. It can be a big balancing act for the promoters. In more recent times, it seems to be more about the drivers than about "the cars". AND the different color schemes for each race, with respect to the die cast sales!
Just some observations,
CBODY67