I've accomplished this using several differing methods. The method I like the most, is to use 2-56, 3-48, or 4-40 blind nuts as a bearing surface/retainer nut for the pulleys. I start by removing the barbs by turning the blind nuts on the lathe to a slightly smaller diameter. While I'm at it, I true up the shank of the nut so it's diameter and roundness are consistent.
I then make up a set of pulleys from steel or brass, usually brass, drilling them to fit as snug as possible to the blind nuts shank and still turn freely. Then I carefully machine the thickness of the pulleys so that they have some end play when installed. I drill the titanium bellcrank to the body diameter of the screws I will be using, and placing the pulleys on the blind nuts, I attach the nuts to the bellcrank "T" style (shank towards the bellcrank) with button head screws. I then grind or file the bolt ends flush. Finish it off by carefully flash soldering the bolt to the blind nut, or use one of the permanent types of loctite to ensure the screw does not back out.
Les