Bd-600 to Bd-11a head unit swap?

Hey guys,
I'm a little new to the supercharger thing, so bear with me....
I recently purchased a used P/D kit w/ the Bd-600 head unit, and due to some severe negligence from the former owner, the impeller has practically torn apart the inside of the housing from a hack-job rebuild gone wrong. Anyways, In lieu of rebuilding it, I have a friend with a recently rebuilt BD-11A head unit for sale at a very cheap price, so i'm just wondering...Are they at all a direct swap, as far as the size of the casing goes? If not, can anyone direct towards a shop that can help me with a new impeller? I've checked out a place called 928 motorsports, and the gentleman I spoke was very helpful, but basically said that if they impeller is shot, there's not much they can do for it. I'm told this is a hard find in general, since Powerdyne won't sell impellers to individual retailers/shops. I hope some, if not all, of this info is at all accurate, so please feel free to steer me in the right direction if it's not. Anyways, thanks in advance for the help.

It is a direct swap. Even the XB-1A is a direct swap. Sounds like that other one is TOAST!:(