Chipboard is hard to repair. Once the moisture has expanded the fibers, it really is hard to fix. The cabinet should be the same dimensions as a Williams 4 player EM. I'd be keeping an eye out for projects on fleabay with the view of replacing the cab and repainting. It is a lot of effort, but if the game is a keeper, then that's the best outcome.
The problem with repairing chipboard is that when you try to paint over sanded areas, it looks uneven. The finish will look out of place.
