https://i.imgur.com/CeyVQHV.jpg

How's this.

I had to resize your image as it was far to large to be seen properly on the board.

While from a collector stand point keeping this all original would be preferred, from a shooters view, relining would be the better way to go.

I doubt you will be able find a gunsmith with .300 reamer. The gun would better serve being relined. I don't think you will find much difference in cost to fully reline to 32-20 than just sleeving the chamber.

If you can sort the .300 reamer out, you still have to deal with finding brass dies and bullets which are not common-in an uncommon bore size.