HT3B Questions

[Woodenhead]

So I somehow managed to destroy my HT3B on the weekend and am looking for a replacement. I found part numbers for Cummins, Schwitzer, Garrett and Holset for HT3Bs with what I think will be a 26cm housing. I have a 26cm housing now which is still usable so if I'm buying a new turbo I might as well find one with a 23cm (or 22cm?) housing and swap them around should I decide to do so.
My questions..
1. Does anyone know if the housings from the various suppliers (Borg Warner, Schwitzwer, Garrett, Holset) are interchangeable?
2. Does anyone have part numbers for HT3B turbos with a 23cm housing?

Thanks,
Mike