bigmessowires said:

 Then to add insult to injury, I couldn't even fit the motherboard with ROM adapter back inside the chassis, because it collided with the cross-piece at the rear just above the motherboard slot. Arghh!

Click to expand...

Back in the day....

The upgrade companies that sold piggy-back upgrades for these machines recommended that you do this:

Turn the machine upside down.   Take the logic board and slide the left or the right side into the frame/chassis slot for that side.  Gently take a flat-head screwdriver and pry the other side of the frame/chassis outwards just enough so that you can slip the other edge of the logic board into its slot.   Voila; logic board installed while avoiding rear cross-bar.