I would be inclined to stay with the standard sized guts, and just remove the ceramic parts to replace with steel. The 360 thrust bearing is a must though
Having had a peek in more detail at mine today I can firmly say that access to the Turbo is ... awkward ... So I would think it best to play safe and go for a rebuild with a few internal mods, rather than big stuff like compressor housings, getting into water and oil lines looks like it would be a nightmare...
As another option ... HKS do apparantly make a bolt-on kit for the RB20DET, might be worth speaking to Andy/Dirk as he's the man for HKS toys
Either way, you can really go far wrong! Good luck dude