In the late 70s when there were very few good heads,there were a lot of engines making power way beyond 7500 rpm. The 327 mouse has been doing this since it came out and is not, was not, and wont ever be limited to 5800 rpm or anywhere near there with stock heads. The 283 had even smaller heads and it can make close to 400 hp at 8,000 rpm and it does not use a 225 duration at 50 cam to do this.
There are better heads than old factory heads,no doubt!!!
Factory heads from the sixties will make power past 7,000 rpm in a 327!!!