I've been using a router setup for many years. I suggest a couple of simplifications and changes. For those who just want to try it, you can run the squares through oak blocks with the progression of holes in them.; Much faster to make up a trial run.
Next, turn the whole shebang so that the shafts are parallel to your bench. Then, you can run the shaft in as far as practical with your drill, stop to remove the adapter from the chuck, and put the drill on the finished end of the shaft and pull it on through. I have been doing that for years. That way you don't have to cut a 36" stick to get 30 inches usable.
And, I can't see any reason to cut a slot for the router. All you need is a hole for the bit to stick up through.
I made steel bushings in various sizes to fit in an aluminum block so I can change to a different shaft size easily. I also mounted a dial indicator so I can move the block the exact amount needed to switch from one size to another. (I don't move the router, just the blocks.
My steel blocks burnish the milled shaft so that no sanding is needed, unless to make a finish stick better or a stain penetrate.
Here's a picture. (My setup mounts to my bench with one bolt and wingnut--changed the mount after these photos.)
Jim Davis