I used a 1/2 inch square piece of hard maple to make a "stand" while I work on the underneath part of the chassis. I removed the tuning scales to keep them safe. I then tape some folded over paper towels to the top of the power transformer and to the top of the HV cage to protest them while inverted.
I used an existing hole in the chassis and bolted on a small cross-member so the stand will stay in place.
Much easier to work on when it is this way.