Before you start sanding away at the frame for no real good reason, send it to me. I will pay the shipping costs. I am serious with the offer. Now, on to the business, the seat clamp ears are brazed to the frame. The "defect" you see is not a defect at all, it is a fit and finish detail that was seen as acceptable by the maker. In my life as a working person I had to deal with this kind of thing over and over again.
Seriously, before you start hacking at the frame, contact me to arrange shipping to me.