Re: making custom dies
The easiest way is to send your reamer print to Neil Jones and he will make a FL size die with shoulder bump bushings in 30 days or less normally. Cost is around $175 with two bushings.
He normally sends you a die that is neck size only for you to shoot the brass a few times and send the die and bras back to him where he fits a custom sized insert in the die and return in in a week or two.
Other factory die makers (Forester, Hornady etc) will do the same. Wait from 8 weeks to 6 months.
The finish reamer idea normally does not work well if at all due to the dimension differences in where you want to squeeze the case in versus just making a FL chamber die tighter all over.
If it is a case that has a Redding body bump die, Jim Carstenson at JLC Precision will take the body bump die, and hone it to your chamber (fired brass again) and make it a FL size die with neck bushings. Cost is $80 and two weeks normally.