Hey mate,
The simplest way would be to source the standard T04 used on the GTS-R and the intercooler piping. Although the turbo is a laggy old-school design, it will be a bit less laggy on an RB25. If you are to go down the aftermarket turbo route, you will need to fabricate lots of stuff. The manifold places the turbo on an odd angle, so both the intake and exhaust pipings will need to be fabricated, and probably changes to the water and oil feeds. The compressor housing will need to be rotated. Not trying to put you off, just show it isn't the simplest of jobs.
I put an aftermarket turbo on my GTS-R and had to get all the fab work done.
As far as sound goes, I found that the manifold didn't howl as much as first thought, but once I dropped some Tomei poncams in it, it wailed like a banshee. Having said that, I have been in cars with cams and 6boost manifolds and the sound is very similar.