I have a Space Invaders and with its heavy double-backglass frame, when I open the backbox, the weight of that and the open lightboard panel tilt the backbox forward enough that I have to keep it braced when open. It's pulling up the neck and the horizontal panel under the neck. I'd like to brace this with something that won't be seen from the outside, and the only thing I can think of is screwing four or so L-brackets to the underside of the horizontal panel and the rear of the inside of the cabinet. Any better ideas?

That's a pretty neat little set of tools but after watching a few youtube videos, I can't quite visualize how it would help an existing cabinet. It would likely come in handy if I was building a cab from scratch though.