Small engine trouble

I have a 14 horse Briggs & Stratton OHV engine in my lawn tractor. Last fall when I was mulching leaves, one of the throttle plate screws worked loose and found its way into the cylinder. I lost all throttle control, so I pulled the carb and found that the screw was missing. There was no noise or any other indication that anything was wrong except for the loss of throttle control.

Now that the weather has turned decent here in the frigid Mid-West, I pulled the head and found this piston and combustion chamber damage. I found no sign of the errant throttle plate screw. Would I be safe to file down the damaged surfaces to free them of sharp edges, then re-gasket and install new throttle plate screws (with thread locker) and button it back up and run it? There don't seem to be any cracks or deep gouges, and the valves are sealing well. I checked with kerosene and they held the liquid. What do you think?