Metal stops, even on the custom motorcycles Ive been around, tend to chip up or get banged and rusty. My Dyno Duece has a nice rubber 'bumper strip' black elec. taped around the flat black top frame tube, it has a raised lip either side of the tape and looks decent. At full stop from either side the fort tube bumps it and no damage done. Sorry that I dont know what the prev. owner used for this, but keep your eye out for possibilities.
I know the hardware store has nice rubber 'feet', kinda cone shaped with a recessed screw center. If located correctly for the bump, on fork or frame tube, the tiny stainless screws shouldnt weaken anything.