I'm not big on after-factory modifications with few exceptions, but these are very interesting. Also, I saw LEDs used in a way behind a very faded backglass that appeared to work well!
Bingo Chime Units:
http://www.ebay.com/itm/New-Old-Stock-Bally-Bingo-Game-Sound-Chime-Kit-with-Add-on-Factory-Kit-/231849933979?hash=item35fb553c9b:g:IoUAAOSwDuJWxg4W
Chris Howard's "Golden Gates" - truly masterful!
http://www.ballybingo.co.uk/Golden%20Gates.html
