3 inch duels is way to big for a 6 cylinder, max size for duels would be about 2in, even then that might be considered a little big, 1 3/4 would be better suited. Considering that most 250 engines only had single exhaust and it was a 2in pipe. Even 2in duels with glass packs can be loud and obnoxious. Check out summitracing, they have a several mufflers under $30 each.
