There is a book called the "Owner's Pictorial Guide For The Care And Understanding Of The Watling Bell Slot Machine" which has detailed pictures and decriptions of the Watling Rol-A-Top mechanism. It should be available from Mead Publishing. Go to
http://www.meadpublishinglasvegas.com/slot_machine_repair.htm to check. Before you start you must get this book. If Mead does not have it then you might try eBay, I have seen them show up there from time to time.
About 14 years ago I documented a restoration of a Mills slot machine on an 8 hour VHS tape. Those tapes have long been sold out but I am looking at putting it out again on a set of DVD discs. The Mills and Watling mechanisms are similiar. The biggest difference is the escaator (the thing that takes the coins) and the jackpot The Watling Jackpot is much simpler than the Mills is.
Go to
http://www.IBuyOldSlots.com and click on the Slot Machine Restoration link to get information about the DVD.
I have been asked to document a Pace, Watling (Rol-A-Top), and Jennings restoration. Sorry, but it is not going to happen. Way too much work involved. I did the Mills project just to see if I could do it.
Your biggest problem is parts. If you are missing anything significant than you could be in big trouble. Watling parts are hard to find.
Tearing a slot machine apart and putting it back together can be a daunting task for the inexperienced. The mechanism consists of hundreds of parts and if you don't put it back together right the thing won't work. If you put the parts back together in the wrong order you will find yourself tearing the mechanism back apart in order to get that other part back in.
If possible, you should try to locate (beg, borrow, steal, etc.) another Watling Rol-A-Top that you can use as a guide. Doing this will save you a ton of time.
If you want to post pictures to this forum of your machine and the mechanism I can probably give you a good idea if you are missing anything major.
One word of warning, if you start this project and get frustrated and quit and just have a half assembled machine and a bucket of parts then your machine has lost a lot of value. This is not an uncommon outcome at al. Take a look at the note at the bottom of the DVD page

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Dave