I can't find anyone to make an adaptor plate, so I gave it a go.
The 986 flywheel has a piolet bearing inside it, so all I need is a machine shop to make a hubcentric adapter from the 13B to the 986 flywheel. Thrust and centering will be changed when I have that piece machined out, but for now this plate is "eyeballed" close enough so I can make motor mounts and an exhaust/intake/coolant pipe routing.
Here are some shrunken pics of the insanity....
And I finished adjusting the rear ride height and welded in the last of the rear... I did the front too, but it looks all the same.