I'd sell the KI guts and restore that to Mario Bros, but that's because MB is a keeper game for me. The sides look to be in pretty good condition! It will cost you though, MB sideart is $95 for the screen printed repro, the screenprinted CP overlay is $60, and you'll still need a bezel and marquee. You can probably get a nice amount for the KI boards and monitor though.
On the bright side, if you MAME it with Nintendo games, and keep that 25" monitor in there horizontally, you can play Mario horizontally, and the other Nintendo games vertically and they will still be about the right size even with black bars on the sides. I'd want to tilt the monitor back to original placement if at all possible.
$500 for that was exhorbitant, but $100 is a pretty good price!
TTYL,
Wade