Sanding the sides down even to the pick shaft, and then rounding them off:


Take it apart, put it back together without the pick:

Round it off:

Countersink:

Ready to rivet:



Buck the rivets:

I just used a hammer & anvil.
From here, you just have to finish sanding the sides down till you get to the pick all the way around, then round off the corners. Sand the rivets flush too.