Its your lucky day. I happen to have a couple empty xarcade boxes (and didn't have to look too hard for my tape measure)
Bottom dimensions are: 21.5" W x 8.125" L
(Thats outside dimensionsusing roughly 1/2" wood)
Side dimensions are Front = 1 3/4" - Back - 3 1/16"
I hope this makes sense, and helps. If you need clarification, I can sketch it out for you.
Also, once you get the top, you shoulc be able to see the small screw holes that attached the top to the frame. They used 1 small L bracked on each side, 3 on the fron, and 2 on the back. (yours may vary).
-Stobe