If they are completely different, there are a few relatively simple ways to get the two to mate up. Firstly, you can make a hybrid bellhousing by combining one that suits the engine with one that suits the gearbox. It takes a bit of care and planning with the ruler, and the manufacture of a simple jig. It is also possible to make the trans fit into the rear of the engine-suitable bellhousing (depending on the style of the gearbox-to-bellhousing connection of course), or making an adapter plate to go between the back of the motor and the gearbox-suitable bellhousing (this is how I put a Supra A340 auto from a 7M onto the back of a landcruiser 1FZ-FE 4.5L 6cyl. If you really want to combine the two and there's no bolt up option, drop me a PM.