Long-time forumites will know that I made my own version of the .375 JDJ using an 8x57 reamer with a .375 throater, and cutting the rim recess. The sizing die is an 8x57 die, softened, and drilled through with a 25/64 drill-bit IIRC.

I use that same sizing die to form both .375 JDJ (reformed .444 Marlin cases) and 9.5 MS (reformed .30-06 brass).

There are slight differences, but after fire-forming both cases can be neck-sized using the same die.