i helped one of the guys at the shop do this very thing last spring. the biggest hangup that he had, was that the tractor had 2 scv's, and the 7700's exhaust manifold didn't fit, had to cut it apart and weld in part of the manifold off of the old engine onto the the "new" engine's manifold,
he also had to rework the air intake tubes for the turbo, besides that, it was just some linkages and some wiring, nothing too major
he ran a straight pipe off the turbo, wasn't loud at all and sounded pretty cool