[OldRestorer]

Simple.

Measure the diameter of the recessed round hole.

Go to Renovated Radios and find the chassis washer closest to the size you measured (but not larger).

Order four of them.

When they come in, place them in the recessions, put your chassis in place being careful not to move the washers, then learn more colorful words as you attempt to get the chassis bolted back in. But you can do it, you just have to be patient and not get in a hurry.

Seriously... I use a little piece o double stick tape for this...