5.9 Magnum exhaust/intake combo help

I bought this RT new in 1999. The horsepower rating on a RT was 250. That was due to a bigger exhaust. Everything else as far as the motor goes is the same as a regular 5.9 Magnum. Same heads etc... No RT heads- and it had the same cam as a regular 5.9. The RT did have a different suspension and different wheels.