nice one... driven an SE4, and they're quite nippy. It misses out on the RWD ceffy's weight distribution though cos its a bit nose heavy (as are GTS4's I suppose). Watch out for the ABS though, had it fail on both my last GTR, and GTS4, and the SE4 I drove was prone to getting air bubbles in the system.
Other than that, a GTR/GTS4 gearbox, new rear diff to match the ratio of the front (auto diff ratio is different to the manual... unless you go the auto route) and RB26 should see it being quite the little sleeper.
Also from memory the late model ceffy's still ran non Consult based ECU's so you'll probably wanna transplant the wiring over from an R32 too.