Also to consider, there are several different types of bump dies. Since your rifle is a custom, you may have access to the reamer. These dies at Borden Rifles are made with the same reamer as the rifle. They size the neck with a bushing and bump the shoulder, two birds with one stone.

Another neck sizing bump die is at Neil Jones Custom Products. For this die, you supply 3 fired cases to the die maker.

I'm sure there are many more options you can look into.