To be running w7 heads in a super stock car, it would have to be one of the modified classes.
The whole car was likely set up around that engine package, and I'm sure part of what the op is seeing is that a class car is often a better, more sophisticated overall "package" than a typical bracket car.

Take a stock eliminator motor out of a good running stocker package and stick it in a similar bracket car and I doubt the ET's would even be close.

Another question I would have is, how close to 900hp was the performance of the car the motor came out of? Did the ET/mph/weight show it to be 900hp?