Pics of progress:
I used 1/4" Al angle for the motor mount. I'm mounting the motor as low as possible, mainly for clearance of the brake post.
I'm going to use the mechanical brakes, so I wasn't able to attach the motor mount to the CD assembly as securely as on my Muggy. I just put one small screw through the CD support near the bottom into the motor mount. But all it needs to do is hold everything in place when I tighten the mount down to the chassis.
I didn't use the Muggy rear brace, because I had no room for it - so I used the Al angle from the top of the motor mount.
I raised the CD assembly up 1/4" with spacers for gear clearance.
Here it is next to my Muggy for size comparison: