Instead of the "standard" 3/8" thick by 3/4" wide bar, I believe some of the Craftsman saws used a thinner bar that was captured in an inverted t-shaped slot. Matching that would be difficult.
Even with a standard miter gauge and one of the commercially-made slots, getting a good fit that produces accurate results is a challenge. Any play in the bar will result in corresponding inaccuracies in the cut.
Plus, on a router table, "square" doesn't have the same meaning or significance as on a table saw. For most operations, a push block or sled, running against the fence, will produce better results.