I needn't have worried! It fits fine, with about 10mm to spare at the tightest spot. Much more everywhere else. Got the transmission roughed in and weighed the car again to help settle on the battery distribution.

Below is the driveshaft adapter. This will allow me to bolt the output of the Lexus transmission to my BMW driveshaft. Milled out the shape from 3/4" 6061 Aluminum. Got most of the way through with my cheapie CNC router before I broke both of my two bits. I finished it by hand. Came out nicely, looking forward to installing it!