Starting with the GMU22 mounting bracket I cut it down to size as it is made for an RV7/9. I then match drilled the holes for the mounting hardware and added a few rivet holes to secure the plate the the shelf. I then removed the bracket and cut the large hole out using a hole saw in the drill press. This worked ok, the hole is slightly over sized, with the mounting bracket the unit should be secure. I then marked and drilled the four corner holes through both the shelf and the longerons. I'm using 6/32nd brass machine screws along with other non ferrous fasteners to secure the shelf. There may be a need to remove it in teh future and I didnt want to try and drill out rivets in a longeron that far back in the tail cone.