Here's my version of this jig with three of it's four modes shown. Note that the top "table" of the jig is plenty wide, providing good support for the router. Also note the Micro-Fence guide - a nice, and expensive, precision edge guide. The router, by the way, is the Dewalt 621 - a nice light 2 1/4 hp variable speed plunge router with an easy to set and easy to micro adjust depth stop system. Also has a dust port built into one of the plunge columns - handy when you're routing at head level.
To use the jig you need a centerline for aligning the part to the jig, the left and right ends of the mortise for setting the left and right router stops and and a line for either the front or back of the mortise to set the fence guide.
Here are some "details" shots that'll fill in some gaps on how this thing is put together.
Still interested? Then let's get to the parts list, the sheet layout and some tips ----->