Completing the motor-mount and installing it took a lot longer than I expected. More than 4 hours last night, but it's done and it seems to work. The culprit was the bracket to hold the driveshaft support. Here's a picture of the mount as of 2 days ago.
That left only one other option: weld nuts in place on the motor mount. This will allow the bracket to be swung in place and still align the bracket properly. So, we installed the mount onto the motor, pushed the driveshaft into the transmission, and attached the driveshaft support using some short bolts (3/8" x 1" long).
Two problems arose:
1) Somehow the entire driveshaft/mount assembly needs to be taken off the motor so the nuts can be welded in place.
2) The driveshaft support bracket, even though it looks beefy enough, actually flexes quite a bit when lateral force is applied.
For #1, our first thought was to slide the bracket off the mounting grooves on the motor, which will also pull the driveshaft out of the transmission at the same time. That didn't pan out - the bolt heads are so snug in the grooves that they don't really slide. So we ended up disconnecting the transmission from the motor (again) to free the driveshaft. Once they were separated, we could take the mount off with the driveshaft attached.
To solve #2, we added a gusset to the bracket. The freshly painted part of the mount in this picture is the gusset. You can see the newly-welded nuts on there, too.
Lower Transmission Mount
This was quite simple. A block of aluminum with two tabbed bolt holes in the top which mate up with the transmission and a single bolt through the center pointing straight down which locates the mount through a hole in the cradle. This is a picture of it before the driveshaft was reinstalled.
Upper Transmission Mount
This is the main torque rod for the transmission. Not yet finished, the plan is to use a piece of angle, some bar stock, and a couple of spacers. More on that later.