That is what I did as well. If you look at this shot from the Magic of Myth exhibit (
http://www.thedentedhelmet.com/gallery/magic-of-myth-2001-12-16-g/p5848-boba-fett-costume.html) you can see the hex portion of the flare nut is longer than the one here, the same problem I had with my "found part". I trimmed the base with a cut-off wheel and wrapped the hex portion with tape, made a small cylinder to keep the center clear, and filled the space with JB Weld to extend them. I think they turned out looking closer to the original:
View attachment 100855
When I was putting these together, I thought the actual sizes are mismatched (they don't really screw together), and you may want to get a larger coupler to match the original.