Years ago when pouring front sights were popular. We did a similar thing with a plastic kids toothbrush, shiney red were the best color to use. When polished they almost glowed. To make it easy we used an old 60° dovetail cutter to cut the notch. Drilled a couple of holes in the sight. Mill cut toothbrush. File fit and used 5 minute epoxy to secure it in a thin cushion of adhesive. If you fit the site into the new dovetail without any clearance the site would fracture while shooting.