2wd cossie is like a stage2, bit it doesn't have a 360degree thrust bearing, but can be mated to the rst exhaust housing very simply.
so in effect like a stage 2.
for me though, i'd find a 4wd cossie turbo and use that instead, that's like a stage3 rst turbo, in that the compressor is much bigger and 0.48 housing is the same, although downpipe will need changing, but will flow much better.
i used a 4wd cossie turbo n my zvh and ran at 23psi without any issues, although i'm now changing to a T34 or similar for a ZT engine.