2.5" would suffice but eventually you will swap in a 451 or a 470 so might start with 3" which as said will be louder and dynomax muffs are good and additional glasspacks alongside the rear springs for resonators will quiet it more as will an X pipe system (dont know why the X pipe system works for quieter but it does). definitely mandrel bends. www.speedwaymotors.com has a nice mandrel universal 2.5" set for cheap (iirc ~$150) with swedged ends that fit together very nice. Myself I run quiet muffs with cable cutouts and by the time they hear (& realize) what I have, the money is already in the hands of a neutral third party and I'm seconds away from nailing it