Now that I have the motor and transmission set in the correct place, I can figure out what to use for motor mounts and transmission mounts. The motor weighs over 175 lbs and the transmission is another 45 lbs or so.
The motor support bracket can be bolted on the bottom as well as higher up, on each side of the motor. I have the motor 'temporarily' supported by ready rod from the upper mounts. That ready rod is hanging the motor from a temporary ladder network sitting on top of the motor module
I began with 1.25 inch aluminum tube straight across the bottom of the motor module, supporting the motor bracket. But it doesn't fit! The tube would raise the motor by perhaps 1/8 of an inch. That's not good, since adjusting the height of the motor should be done with spacers, not by modifying the bracket or supports ... well, it was a good try!
Scrounging through my metal storage, I locate a couple of pieces (mismatched) of angle iron. They appear to be about the right length - 4 feet or so. The first is cut and fits pretty well. The second is cut and does not fit .. somehow ... there is interference. The interference results from the angle iron being 1.5 inches high on one side and 1 inch on the other.
A simple exchange of ends and the interference is gone.
Drill a hole for a bolt into the frame on each end of the angle irons, but don't put the holes into the frame. The holes in the frame will be slotted .. later
Spacers ... it looks like about an inch. I took small lengths of 1 inch steel tube. That's not quite enough. Add a couple of washers on each ... that's pretty close. Check the height and it appears to be 1.25 inches! that's where I started .. hmmm. Remove the spacers and use 1.25 inch tube. It works! Drill and bolt.
The transmission support is a bit further away from the side of the motor module. I expect that this support will be a bit more complicated.
Start off with the biggest tube I have - 4 inch. Using vertical runs of 1.25 inch tube as supports, then attaching the 4 inch tube to the 1.25 inch ... the 4 inch tube ALMOST fits between the 1.25 inch tube and the transmission mount .. with a bit of interference. After spending a bit of time with a jiffy marker ... and a jigsaw. A small pile of aluminum shavings .. some filing ... it just won't fit! The whole idea is to make it EASY to adjust the height of the transmission as required. Moving the front to back position is a bit less likely, so it can be a bit harder to do. A 3D cut into the 4 inch tube weakens the 4 inch tube, and is not very flexible for small changes or adjustments to the vertical height of the transmission.
Ok ... back off and regroup. The vertical 1.25 inch tube will fit BESIDE the 4 inch tube. How about that? Then I can add 1.25 inch tube bolted to the 4 inch, that the transmission bolt will go through. Changing 2 short (3 inch) lengths of 1.25 inch tube to make adjustments is not too bad. Moving the transmission left or right is done with shims. Up and down with new holes and replacements for the short tubes. It's good enough for now.
All of these tubes are bolted together with grade 8 bolts and nuts. As the video mentions - that bracket would support an OX.
Youtube video