Aside from the fact that he completely replaced the whole tunnel (for reasons other than the exhaust), I seriously doubt that what he did with the exhaust was all that much work.
If you just want to get the exhaust down under the track, buy a couple of those kind of cans from an auto store (make sure they're stainless), cut the pipes, weld the new cans on pointing down.
You would probably also want to block off the hole under the seat so that snow doesn't fill it up.... a piece of sheet aluminum riveted in there should suffice.
If you don't even want cans, just weld elbows on the pipes.