Take a low to mid pack stocker type build.
Put in a “real” cam, good intake and carb...... it’s not going to make less power.
One really important element of the Stocker build is the converter.
And if you’re chasing ET’s...... the ET friendly converter isn’t going to be any good on the street.
Same goes for the gears.
The thing about looking at stockers and there performance, is to take note of all the things they don’t use to get it....... and then look to see if you can apply some of that thought process to your not-a-Stocker.
If it’s a “street” car, that will be seeing some real street duty..... then you just start piling on the compromises........ which results in comparatively poorer performance(for the sum of the parts).