If you did not have the smith make a set of dies, then my suggestion is get a copy of his reamer print and send it to Neil Jones. He will make a set of custom seater and FL size die that also does a shoulder bump. He is the only one who has the shoulder bump die and bushings. He will send you a neck size die only first and let you load and fire a couple cases. You send the die and cases back to him, he hones a custom insert for the FL die and inserts it and sends back in about 2 weeks. A set will run you about $275-300 and 30 days.
Your other choice is to find someone who has a set of dies can load you about 5 rounds and let you fire them, to fire form and then refire at full size. Send 3 fired cases to Forester Bonanza or Hornady and let them make you a set of dies. Might be less money and maybe the same timeframe if you are lucky.
You can buy an intemediate bushing to size the neck down about half way and then go one final step.
IMO Imperial size die lube is the best for this. Also when you fire form a small swipe of this on the neck shoulder junction will help the shoulders fireform at the sharp angle. You will want the bullet seated long into the lands to get the case centered when fireforming. You want a slight crush fit (hard feel) when closing the bolt. The other way is to leave a small step on the shoulder when sizing down to use that to fit the chamber. Go to www.6mmbr.com
and they have pics of that under fireforming the 6br to the Dasher. Same process only larger (much) case.
I imagine you will find the load for the final improved to be RL 25 in/around about 90-97 grs and same with Norma MRP2, which I prefer. Buy your powder in large quantities of the same lot. RL powders are known to be temp sensitive.
cannot remember my fireforming loads right now, but I am sure that others will chime in with them and other powders.