Are you crazy. Do not polish the bridge with rubber abrasives. The lines over the bridge help to catch OIL to cool down the bridge.
If your piston is seizing on the bridge, put the piston & cylinder back together. Take a pencil, with the piston a TDC and scribe a line on the pison in side the exhaust showing the thickness of the bridge on the piston. Take the piston out and drill 3 small holes between the two lines on the piston. This will help cool down the bridge port and prevent seizing.
Note: Try Motul Karking Pro : Rated up to 23,000rpm's Premix
(2) - Motul 600 Premix
(3) - Motul 510 Premix/Injection
Added Speed