This EBay seller makes all sorts of adapters for turbo inlet & outlet bolt patterns, and will CNC machine custom-made adapters for just about any application, so if you want to mount an oddball turbo to your engine and don't want to make an adapter yourself, check him out...
EBAY LINK
yes it should. You would be making a DP right?
yes, I would love to buy that flange to go from 2.5 to 3" if it was that easy and then weld the 3" DP on to that.