We're unsure of the best way to create a coupler, spacer plate, and mounting plate. So we bought some 1/2" plywood to use as templates. We drilled bolt holes in the mounting plate to match the transmission bell housing and a two inch hole in the middle to allow for the coupler. To figure out where to drill the holes, we used old, thick motor oil leftover from our ICE and rimmed the bolt holes on the bell housing. Then we stuck the plywood onto the bell housing which created a mirror image. It sounds easier than it looks.
Here's the motor side spacer plate mated to the motor using 4 bolts. Again, we had a bit of trouble, but managed to find the holes.

Controller

24V-120V 600A Kelley Controller

Motor Arrives

Warp 9 Motor by Netgain
Transmission Bell Housing