With the inner jaw fastened to the bench, I used the router to flush-trim the jaw to the benchtop, across the top and down the sides adjacent to the top (stopping short of the discontinuity between the top and the legs). I'd thought this would be the best way to match up the jaw against the top, but I'd not do it this way again. It was very difficult to hold the router tight against the face of the jaw, and the result was a surface that wasn't as even as I had hoped.
The base needs to be as wide as the sum of width of the guide strip and the distance from the edge of the shoe, plus a bit extra, With my saw, the overhang is 3-1/2", so I made my guide strip 5-1/2" wide. The distance between from the edge of the shoe to the blade is about 4-1/2", so the base needs to be at least 10" wide. Since I was working with a 24" wide sheet, I just sliced it down the middle.
Grizzly is a company currently undergoing an upheaval. This brand was once known as a manufacturer of professional grade tools and equipment for woodworking products. Though, in recent years, that reputation has begun to slip a bit since being bought by the Chinese company SIEG. These days, whether the Grizzly product stands up to its previous standards of excellence often has more to do with what you are buying than the company itself.