I know you mentioned you already had some hardware you are wanting to use for this, but if the cost of the parts starts to add up to $40 you might want to consider an Arduino-like microcontroller. The ATMega128 can be found for as little at $39 w/free shipping on ebay.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270562834281#ht_992wt_1165 Like I mentioned in the last post, there are some cheaper clone boards (freeduino, perhaps) that were even cheaper.
It has 12 PWM connections (could be used for 4 individual RGB leds/led banks, or ), 36 Digital I/O (3 digits * 7 segments = 21, 6 for ball sensors, and a handful left over for other lights/buttons), and 16 analog inputs for whatever you wanted. They're easily programmed via a computer, you write your program, connect the board via USB which appears as a thumb drive, and then copy the compiled program to drive. I've not done it personally, but have heard good things about it.
If you scan this thread and the other one I pointed out, there have been some "blueprints" drawn up by the awesome UncleT with measurements. They have been the de-facto standard the DIY skees here have been based off of. I think the images are also available on his website, I believe. He's a great guy and I bet if you're unable to find the information in what is already posted, if you email or PM him I'm sure he'll be glad to help out. I did a quick search, and he does have that info posted. A page of photos is here
http://unclet.arcadecontrols.com/SkeeBall/SkeeballPics1.html and the one with the information you'll need to determine the gutter size is
http://unclet.arcadecontrols.com/SkeeBall/pics1/023-SkeeBall.jpg I've read the "real" skeeball material for the rings is made from the same material as the whitewall part of whitewall tires by Goodyear. Incidentally, you can get real Skeeball rings from Happ, but they're not cheap. You need to be careful about picking a material that is too tough--it might not withstand the stress of repeated ball impacts and crack, or even worse take some chunks out of the balls.
Good luck in your search. Please let us know what you end up picking out and and how well it works for you.
--James