A larger diameter stud base would be easier, its much more difficult to reduce the diameter of an existing hole then to expand the diameter an existing hole. Enlarging a hole is a simple drill or ream process that you can do to the already existing holes.

To reduce the hole diameter requires welding or plugging the existing hole, and re-drilling to the new diameter or relocate the hole to a new position on the drum and hub.

This is one of the issues we face when we attempt to retain the 60+ year old equipment. We either seek out usable "experienced" replacement parts, or retro fit the original components with currently available parts, doing what ever modifications are required, or we update the entire process with a different system we hope to be able to get parts for well into the future.

Your going through a lot of effort for something you tell us your going to replace with disc brakes. I know I probably sound like a fool, but I've been playing this game for more then 40 years. There are many reasons why one of the first things I do with old cars and trucks is a disc brake conversion, what you are experiencing is only one of them. Gene