Bolt the legs to a square base and paint the base black or something so it does not stick out. This will ensure the thing does not tip over. The legs will bolt to this wooden square base and it will give the illusion that the feet are holding up the control panel. The player could actually place their feet on this wooden base while playing which would give it even more stability. (see attached pic).
Without doing something like this, I would not feel comfortable watching someone jerk the joystick back and forth while playing a Mame game. I would be to worried that the whole control panel would tip over.
You do know that SpongeBob does not have 4 legs right? Perhaps build a control panel where SpongeBob and Squidward are standing together. Have two legs from SpongeBob and two legs from Squidward holding the control panel up. Or perhaps have SpongeBob holding a cane or something to give is three supports (2 legs and one cane). How good of an artist/sculptor are you?
Now, if I was going to make a "bartop" for SpongeBob, I would place the cabinet on the bar and have SpongeBob's legs/feet hang over the bar.
Ok, I will shut up now ......
