I'm in the process of adding a router extension to my T.S. too. I looked at various ones I can purchase or make and have decided to purchase the Peachtree cast iron extension. I already have a JessEm Rout-R-II lift to drop into it and a couple of routers, but decided to replace my MDF stand alone router table with a T.S. extension. My T.S. is a beast, an old Craftsman cast iron top contractor with 3 cast iron extensions, and has a Vega 50" fence system. Not pretty, but it works.
Don't know if I can shift all 3 existing extensions to one side and put the router on the other side or if that's going to be just too darn big. Or will require new legs to prevent tipping. The Vega fence sticks out past the 2nd RH extension now and determines the overall width for storing when not in use.
Craftsman 113.29992 Table saw, Craftsman 10" band saw, H. F. 10" drill press, MicroLux 7"x16" lathe, Dewalt 734 planer & Craftsman 6 1/8" jointer