You're probably looking at 500hp at the crank, or roughly 435whp. That's should be well within reason for 10psi on a motor that made 287hp crank to begin with. UTEC for these cars is pretty neat. I have no idea who tunes them around here, though. You might try a forum like my350z.com for that info.

That tranny and diff should hold that power without a problem. You might get some wheel hop, but most of the Mustang IRS rules apply there (solid bushings). By the way, welcome to a modern chassis that doesn't need subframe connectors. This is one of the stiffest chassis that Nissan makes. One last note, the limited slip diff isn't like your stang one. The basic Nismo diff is a clutch-type unit, where the stock one uses a viscous coupling.