Well I see two possibilities.
A. Have some kind of mating couple fabbed to connect the new engine
to the transmission
B. If you buy a Betamarine get one of the V-drives that they have as an option. The only problem I see with this is that they may not angle the down angle you want. If you can get close you can adjust the angle of the engine
beds to get the rest of the way.
Out of couriousity what kind of boat?
A house is but a boat so poorly built and so firmly run aground you would never try to refloat it.