Framebuilders - braze-on position for ft. derailleur.

I bought a NOS ft Zeus derailleur for an old Zeus frame and want to do the best job I can at brazing on correctly. Any guidlines for that? I seem to remember for old derailleurs the outside of the cage needed to just clear the large ring, say about a millimeter as it passed over the teeth. Your input is appreciated,

Thanks,

Any reason not to use a clamp-on derailleur? Braze-on FDs can be limiting when changing chainring sizes.

trying to decide where to put the boss is a pain, even when the data is published. It really depends on what chainring sizes you think you will use.

If you set the slot to hold the FD for a 53-42 you should be able to later switch to a compact 50-34 and have the FD work.

Thanks for the responses. To answer John's question, I could not find a Zeus clamp-on derailleur at a reasonable price within a reasonable time spent on @#$% eBay. Plus, I was looking for an excuse to practice brazing something on this old Zeus frame from the 70's. This bike will have a 53 tooth large ring as long as I have it, so I won't have to worry about that. I will just go by the old school method and clamp it on with a hose clamp and flow that brass into the space and hope for the best. Again, I thank you all for your responses.

The Shimano investment-cast FD braze-on has a small pin that holds it in position while you braze. Plus, it looks a lot cooler than the simple stamped braze-ons from Campy, etc.