I'm also a big fan of Smash TV. In fact, it's because of that one game that I got involved with this whole hobby at all. I started out trying to buy my own Smash TV machine. After I found out how much they usually sell for, I started researching mame and ended up here.
I thought you might find it useful to know that the spacing between each player's left and right joystick on a full sized (25" monitor) Smash TV machine is 6.5 inches center to center.
I've made a Microsoft Visio 2002 drawing of a Smash TV control panel. Everything is correct except for the distance of the 1 and 2 player start buttons from the top edge. The person who gave me the measurements for the rest of the control panel omitted that measurement...
http://www.3feetunder.com/krick/mame/visio_smash_tv_unfinished.zipAnd in case your also a Robotron fan, the spacing between the two joysticks on a Robotron machine is 10 inches center to center.
Here's a thread where I talk about possible 4 joystick (player) layouts and their fitness for playing Smash TV...
http://www.arcadecontrols.org/yabbse/index.php?board=1;action=display;threadid=16720I've been fiddling with a design for my control panel trying to incorporate 4 joysticks and 2 trackballs. Keep in mind that it's a work in progress but here's what I've come up with so far. I don't know if this is the design I'll use or not...

I hope some of this helps.
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Krick