The most Common Side Rails used on our Williams widebody Virtual Pinball Cabinet are the original Williams stainless steel side rails Part number A-12359-3. These can be found at either Pinball Life or Marco Pinball. It is important to remember when installing these be sure to install them while your Backbox is removed.
So lets get started.
First lets remove our backbox and line the side rail up so that the front edge of the side rail is flush with the front edge of our cabinet
After that make sure the rear piece of the side rail is flush with the rear of the main cabinet playfield like below.
Many people like to use double sided tape underneath the side rail to help keep it in place. If you would like to do this be sure to review mjrnets section on installing side rails.
http://mjrnet.org/pinscape/BuildGuideV2/BuildGuide.php?sid=cabHardware
In my experience you only need a small amount of the tape.
After the side rail are installed and you are happy with the alignment go ahead and attach them in the front using a 8-32 x 1-1/4" Side Rail Carriage Bolt Part Number 4308-01123-18 and 8-32 Black Nylon Insert Lock Nuts Part Number 240-5102-00B and a washer. These items can also be found at Pinball Life or Marco Pinball. As far as the rear section any standard style wood screw will work.
Awesome you are now done and ready reinstall your Backbox!!!!