If you rotate the wheels on your motors you'll notice that the bolts holding it in place do not turn along.

Or at least the ones I have that look exactly the same don't.

On my feather I used a longer bolt and a spacer to mount the motors directly to the sidearmour. With a couple of holes in that angle iron you could than attach your baseplate to that and the sidearmour making a rigid box with your motors supported front and rear.