The SRT "manifolds" are actually a shorty header, that s why they flow a little more but a little more ex flow is not going to translate into much HP on a basic 5.7 and it will be obvious to the inspectors and is not CARB legal, either get a long tube CARB legal header (if there is such a thing) or don't bother.

Another decent compromise would be if you can find a 6.1 long block to slide in there with a good tune... cheaper than a stroker but still have OE reliability. Not super obvious to someone poking around under th hood especially if you paint it black.