To make a featherboard, cut your board at 60 degrees. Drill 7/16” holes and scroll saw between holes to make your two slots. Using a bandsaw fence, cut notches 3 inches long. Try cutting around 7/64” center to center. Use a soft wood so the fingers will flex easily.
To attach to miter slot, cut a length of hardwood that fits snug in the slot. Drill two 17/64” holes to match slots in featherboard. Countersink the bottom side for a flat head for a ¼-20 screw. Also drill two 3/16” holes two inches beyond the 17/64” holes. These are to prevent the board from splitting. Scroll saw a slot in between the 3/16” holes.
As you tighten the knobs the flat head screws will pull up and spread the hardwood tight into the miter slot.