Wow, I thought I had taken more pictures of this process. But it appears I didn't. But here's the conversion process for the donor transmission, to change it from all-wheel drive in the donor car to rear-wheel drive only in the kit.
In this pic, you can see a stub axle coming off the side of the transmission, at the left side of the frame. In the donor, that (and the one on the other side) sent power to the front wheels. The driveshaft at the tail of the transmission, to the right of the frame, powered a drive shaft for the rear wheels.
I don't need that second part. Because I am relocating the transmission from the front of the donor car to the rear of the kit, what used to feed the front wheels will feed the rear wheels instead - and the rear drive shaft just won't exist.
This locking collar will go where the center differential used to be, preventing the rear shaft from turning at all. This effectively redirects all the power to the formerly-front axles.
In order to get this in, I took off the last segment of the transmission case, pulled out two geared shafts (I swear I thought I had pics) and a differential, and then installed that collar to lock the rear of the transmission.
And this plate blocks off the tail end where the rear driveshaft used to go. The 25 mm bolts supplied with the kit ended up being too long, but I was able to source some 20mm bolts locally. A little RTV to seal it all up, and the transmission conversion is done!
This coming weekend, I am hoping to make progress of getting the engine and transmission mated, in prep for the first (of many, I am sure!) introductions to the frame.