> My original plan had been to use their standard 1U folded sheet metal design, but I discovered too late, after boards were ordered, that it wasn’t going to work due to the 5mm corner mounting holes being inside the keepout area for the rear bend.

I wonder if a less annoying solution would have been to omit the mounting holes and then drill and tap them after the fact, possibly at a slight angle if the metal is out of plane there.