I've heard many stories like that... Every design makes power differently and technology has come a long way in the Pontiac world. If you wanna go fast on the cheap, build a Chevy. If you wanna spend way more money and be different, build a poncho.
I was told by a few people that I drove the 389 all wrong. I tried to run it way up in the Rev's and it just would not run there.
It was Dyno tuned (yes, we had chassis Dyno's back then) to run the best it could. The headers really helped. I was just used to zinging my engines north of 7k when I ran them. If you have ever spent any time behind a really well tuned L-79 3 peddle Nova you will understand what I am talking about.
The Poncho was happy in the mid to high 5's. The Bird was never happy.
I did the same thing to the few MoPars I owned.