The exhaust can just be enlarged. Going dual isn't going to help and I would be, it would actualy hurt. At 2-1/2 inch pipe size, it is plenty for the engine size and HP level of the engine.
well the idea bhind doin the Y pipe was that when the 360 goes in, i would reuse the pipes, mufflers, tips, and just cut the pipes where it straightens out an run new pipes from the 360 manifolds/header(dunno yet) to meet the rest of the exhaust