Smart move. The converter hub needs to be as smooth as a crank journal. Babbitt bushings are typical of what builders use, but I also know some that prefer the bronze bushing. Most if not all transmission, Chrysler, Ford, GM and a lot of others from the factory use babbitt bushings. And it's a wise idea to send it back, and have them replace the hub. The converter shop we had where I worked, replaced ALL hubs on converters, stock, high performance, diesel or industrial when we rebuilt them.