First off let me say this; The best way to alter reamer dimensions is to send it to Dave Kiff and tell him what you want! If you need it today though, you can do it yourself by hand if you are semiskilled. I am, at best, semi-skilled so I can speak on this!
First, you can set the reamer up in a test fixture or between centers in the lathe. I'll assume we're using the lathe.So , set the reamer between centers using a dead center at both ends. We won't be turning the spindle and I prefer to lock it in place if possible.
Next, set up a .0001" indicator. In this case we're reducing the neck diameter so we set the point of the dial to rest in the center of the neck portion of the reamer. It's not uncommon to find, as we rotate the reamer, a bit of variation in the cutting edges. I've seen up to 7/10ths.
Now, simply take a hone and reduce the height of each edge by half the amount we want to reduce the diameter. If the heights do vary we will, of course remove more or less to make them all the same. I use one of those EZ-lap diamond hones unitl I'm to within .0002 of the height I'm looking for then switch to a very fine ceramic hone for the last bit. It's easy to get within .00005 on the dial to the height I'm after. Well actually, it's not all that easy. In fact it's kind of tedious but I do it quite often so it can't be that tough!
All that remains is to move the indicator to the front of the neck and check there and to the rear portion of the neck to check there. Use a little radiused hone to clean up the juncture of the neck and shoulder and there it is, custom reamer!
When it's all said and done we'll have a better appreciation for the services of our reamer grinders and a better understanding of how things used to be done. Regards, Bill.

Another good "Leeper" post.

Thanks,
Pat

Bill, The only thing to add to that is to skip the hard Arkansas and use the E-Z 's that come with the blue handle.
There is less rubbing that way.