Hey CadNova,
Welcome to the board. The Nova/Cadillac swap has been done before. Unfortunately I cannot help you with specific details of the swap, but I believe that it is fairly straight forward as far as swaps go. You might want to try to contact this board member to see if he can provide some details.
http://caddy500.com/index.php?action=profile;u=34Manual tranny's behind the Cadillac engine have also been done. It ends up being fairly expensive by the time you buy the trick flywheel, clutch & bell-housing. The tail end of the crankshaft needs to be drilled to accept a carrier bearing & the input shaft of the trans. Then you need to locate a tranny that has the torque handling capabilities to survive.
The bell-housing mounting pattern to the Cadillac engine is commonly referred to as the "BOP Pattern". It stands for Buick, Olds & Pontiac, as they share the same bolt pattern. I suppose it should be refereed to as BOP&C.
Good luck on your swap & please keep us posted on your progress.
Thanks
~JM~