I have been wanting to replace the front derailleur on my old Trek 1000. The derailler it came with was the original stock Suntour Blaze. Many of the other components on the bike had already been ugraded. I had bought a Shimano 105 front derailleur (FD-5600) at one point, but it was a newer one designed for the newer narrower 9/10 speed chains. But it was the only Shimano 105 I could find that had a clamp size of 34.9mm. There were some other derailleurs from that period, but they were for frames with braze fittings on the frame
I had given up for a while on replacing the front derailleur. But then I discovered that Shimano make a Braze On Adaptor for a 34.9mm seat tube! Sweet! And I could buy the fitting for under $15. Then I would be able to use any of the older braze-on front derailleurs. I ordered the adaptor. Then I started looking for front derailluers. I decided to get a Shimano Ultegra braze-on front derailluer. Actually, at the time, the Ultregra stuff was called Shimano 600. But it’s Ultegra. I got a great deal on a Shimano 600 (Ultegra) fd-6401 front derailleur. With shipping, it cost $15. Both the clamp braze on adaptor and the derailleur came extraodinarily fast. Installation was easy. Now I have an Ultegra front derailleur. I am looking at upgrading the rear 105 derailluer to Ultegra as well. And maybe the brakes, and shifters if I can find good deals on them.