I'm not sure how to bolt the Porsche transmission to the Grand National engine, but I'm assuming you would need a new custom bellhousing, and possibly a different sized input shaft, or shaft adapter.
The 3-rotor Delorean has a Porsche 6-speed in it, you may want to consider contacting the creator of it, Jim, at
[email protected] to find out what needs to be modified to fit the transmission into a Delorean chassis.