I don't really think mating the VR6 to the Subaru 5MT transmission is the best idea. The VR6 is a transverse mounted engine, and the 5MT is designed for a longitudinally mounted engine. While it might technically be possible to mate them, that's prob the least efficient use of the very limited space in the 818, and I just don't see it working.

If you really want a VR6, I think using it's transmission is a far better idea. You could mount the VR6 transversely - like it's designed to be mounted - and make much better use of the space. You might have to make some modifications, but I think the result will be better in the long run.