for the circle jig...
And the rod length can be changed to what you need...I have both the Craftsman and Bosch edge guides. The Bosch is far and away the more useful and better designed.
It comes with an infinitely adjustable circle cutting attachment (within its range...up to 32")
At approx. 2 min into this vid... https://www.youtube.com/watch?v=O4kSqS1K7SY .it illustrates the circle cutting function.
Seems like it'd be a very simple project to make a DIY rig.
I measured the Craftsman guide rods on mine, they're .048" ie 1/4" rod.
And the rod distance apart (on mine) is 4 7/8" on ctrs.
Check with your router to confirm, but those really are all the measurements you need to whip one up.
Other members have posted pics of their DIY edge/circle cutting guides in the past.