Quick answers from my quick searches:
Every GM 3800 uses a 60º V6 bellhousing pattern. To get a 3800 to attach to a 6-speed transmission, you need an adapter.
That adapter goes on a T56, and then you can bolt a 3800 or some such engine to it.
For the M90, you can go a couple different ways. There is the Australian route that will directly bolt up to the 3800'* heads, or you can entirely cut off the TB part of the supercharger, weld on a 90-180º pipe, and weld onto that a TB adapter. I've actually seen that done (in person, so no pics), but generally anything is possible.
Whatever you end up doing, please take tons of pictures!