I modeled a possible top-mount sled attachment. This has the benefit of being removable for experimentation and easier to align (and it looks like a ship from Star Trek).
Here’s a link if you want to play with the model. The sled is 18" (mm due to scaling issues, but same diff) and the “router” in the middle is 7".
None of the bar (or triangle) lengths matter much, as long as all holes are the same distance as their same-colored peers.
Adjustable linkages were mentioned in an above post, and if the 3-part blue arms were bolted together with the internal holes elongated, we could possibly have the adjustment that @blurfl and @pillageTHENburn are talking about.