Thanks again to Bryan Kelly, jathomp22, and my friend James Ahlschwede for making this video possible. Hope this explains the process of screening a WPC backbox. The process is nearly identical for the smaller patent screen except there is no need for a cleat since the screen can rest again the rails.
PM for interest in buying a set of screens.
Link to original thread with pictures http://pinside.com/pinball/forum/topic/fs-williams-wpc-backbox-warningpatent-silk-screens