feed assemblies

I have a brand new Lamy nib and managed to source a feed from China (by way of Etsy). I now have both but found the feed a pressure fit (no threads) and I've never done that before. The majority of the feed that will sit within the section is 6.3mm OD, but it has one "bump out" area that...

I received an email this evening with the following proposition. I had not considered the advantage of having a die to make a mandrel for turning. Before I make myself even crazier than I already am, would this be a valuable idea? Would we be better off just having some custom mandrels made...