Everyone did it. In the Pony car days, the 'Stang, the Camaro and the 'Cuda were all competing for T/A Glory with "small" displacement V8's (302-340 ci). Having driven a bone stock Z/28 302 and an original T/A 'Cuda, I can tell you that both of these produced power FAR North of their advertised 290 HP. I mean 290??? C'mon, both of those were not even close! I've read dyno test reports from back in the day where each of them were putting out in excess 375 HP, and the Boss 302 (also T/A spec) was supposed to be right in the same arena. The GM big block cars were even more under-rated.
It was a FUN era to learn to drive in though. I'm not quite old enough to have driven them NEW but, they weren't very old when I got to play with them. I'm lucky to be alive!
When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.