One of these has a mistake you can’t see in the photos and needs to be remade. One of the holes is off by 1/10th of an inch which is likely more than enough for the motor mount not to slide in properly so I ordered a tube of the same dimensions and alloy to make a new one. The rest came out perfectly. It’s one of the ones in the second photo in the dark primer.
The next job is to drill the holes for mounting them to the square pockets which means removing all the bolts on the bottom two corners and running them through the motor mounts.