I did this with my CA18DET about 3 years ago. I still have some of the parts. I broke the shaft in the turbo when I tried to dissassemble it for service, and I gave the exhaust housing to my brother. This event is what started my project.
I recommend buying an aftermarket turbo manifold to cure any clearance issues. Shop around for your turbo, and use the saved money to buy the manifold.
The S14 T28 doesn't require water line changes, but the oil outlet flange might be different, I can't remember.
I put a 5mm spacer between the manifold and the turbo (for heat clearance), and used S14 200SX studs from it's turbo manifold (Got them through nissan)
The dump pipe should fit straight on. But you will need to elongate one of the holes by ~2m in the dump pipe, as the bolt pattern is slightly different. The spacer just means the exhaust will hang down 5mm more, and requires 2 turbo gaskets.
The output pipe on the intake side, is in completely the wrong direction, you'll need to sort that out, and the low pressure side of the intake is a different diameter etc, and you might need to invent some piping there too.
I just read GT28, that could be a different story. Also note that Ballraced turbos can require an oil restrictor, so the bearing is not pressurised with oil (which affects turbo lag).
www.silviansw.com guys recommend a 0.7-1.0mm hole, instead of the factory 4mm. This opinion is echoed by GCG Turbos and HKS.
Hope this helps.
Chris
ps. If you ever decide to disassemble a turbo, please remember the nut on the turbo shaft is "reverse threaded"
