Yeah someone on the R31 Skyline club had a replica made. Can't remember who. Pretty much just get someone to make the longest equal length runners that will fit in the engine bay.
Yes the car is a GTS-R but the manifolds were made by Gibson (slightly different to GTS-R, sound is pretty much the same I believe). If you were to throw a GTS-R manifold on your RB, it would sound pretty much the same.