I did a test run the other day, then made some modifications today:
I modified the donut and added a collar.
I swapped out the old dumbbell for a barrel bolt with steel spacers. A 1/4" threaded rod now passes up from the base of the arm and is held tight by a clamping knob. The donut is a nylon furniture slider with a soft collar with a 1" diameter. It had a convenient pilot hole that I enlarged with a 1" brad bit on my drill press. I like that it had some convenient mounting screws to hold it all in place.
My test run demonstrated that the vibration from the laminate trimmer will cause any loose parts to rattle. I was able to get a serviceable ledge on both a test 2x4 and an MDF bending form (that never gets used) but after a few passes the rods that hold the adjustable portion true worked loose. I need to get another clamping knob.
The biggest problem is that the laminate trimmer does not extend any further. It barely extends past the donut. Time to upgrade to a better router. SMH.