Unfortunately the cardboard box didn't really have the strength to hold he monitor in place.  But I wasn't ready to build the final cabinet (i.e. spend $$ on materials).  Fortunately I was able to build a replacement using a 12x24 shelf cut along the diagonal and some Ikea scraps which were the perfect length.  I used some "hockey tape" to decorate the cut edge.  (Not sure what I'm going to do on the final version as I don't feel like spending the $$ to buy the slot cutter to use T moulding.)

Then I one of the local 'cade shops decided to have a sale, so I picked up a Sanwa joystick for half price along with buttons, a controller & wiring.  This past weekend I made a simple control panel out of a scrap piece of 3/4" MDF - both to mount the buttons so I could start using them, but also to test out my woodworking skills for the joystick mount.  For the final version I'm planning on having a 1/8" top-cover to hide the mounting plate & buttons.

So far it's worked out great except I had planned to use the player buttons to both insert a coin and start the game.  Unfortunately some games don't like this configuration, so it looks like I'll need to have a dedicated coin button. 

I've ordered Logitech S150 USB speakers and they should be showing up this week next month.  I lucked out as the cheap "USB powered" speakers I was planning on using still used a headphone jack for audio rather than USB!  (This actually turns out to be quite common for "USB speakers".)  Before I found the S150 I was worried that I'd have to go to a more costly option.

I'm still going through the games.  There's a lot of games which are playable, but not at full FPS.  While this doesn't impact the gameplay, it also means the RPi doesn't have the CPU power for good audio.

I'm also mulling over how to finish the cabinet.  While I'd love to get some custom vinyl made, I'm not sure of the cost.  Plenty of time to figure that out later!