The compressor wheel has nothing to do with what size shaft the turbo has inside the core.

Has the comp housing got bolt holes/fixings?

The only way to tell for sure is ask who the person who built it, or take it apart and have alook. There are soooooo many Turbo's that come on different cars that you could never be 100% sure. E.g A Saab, Volvo has the same size T3 shaft, yet the compressor wheels are slightly different.

Have you got a picture of the turbo in question as this may help us tell you what it is.

HTH
Regards