I finished making a new back. The original had several flaws besides the upper mounting holes being enlarged as to be ineffective.
The right side back brace was located too high and interfered with the upper mounting boss. This skewed the whole back and it warped badly from the chassis screws forcing the back back into position. With the brace too high this brought the whole edge down low and the bottom of the back overlapped the bottom of the cabinet. Also somewhere along the way, the interlock on the chassis was changed out probably because of the extreme pressure of the mal-aligned back.
All of these problems were corrected with the new back. I also added 2 1/16 ply shims to the back which runs up against the chassis so when the mounting screws are tightened, they won't warp the back. This is due to the metal interlock bracket. I used some Dewalt brad-point drill bits to drill the holes.
I changed the power cord and made up some new labels too.