The standard two-die set is all you need for forming and loading. It will push the 9.3x74R shoulder back to position for the .400/360. Then you trim the case to 2.740".
One thing you will need is a neck reamer die. I found that my cases formed from 9.3 brass had a distinct thick ring at the base of the neck where the brass thickens at the original junction of the neck and shoulder. This is removed with the reamer die and reamer.
In fact, once you get your reamer die it's easiest to use it for forming the new shoulder and then reaming in the same operation. In that event, trim your cases before forming.
If your rifle is a William Evans pm me the serial #. I've owned 2 Evans 400/360s. Both were exceptionally accurate and I'd be happy to share the load data with you.
