Unfortunately there is nothing that can be done. You should send it to me so that it can be properly disposed of.

Seriously, I would get a chamber cast to see what the shell length woud be just to be sure you aren't putting a shell in that's longer than the chamber. You can most certainly shoot the shorter shells in it with no problem. I shoot 2-3/4 loads in a 3 inch chamber all the time and have for years. It's really a very common practice. In fact I rarely shoot 3" loads.

Whatever you do DON'T ALTER THE GUN! You will ruin it as far as it's collectability. You will NEVER recoup your investment should you ever decide to sell it.