I'm new to frame modification and brazing. I'm brazing together two small racks, one for a handlebar bag and one for a saddle bag. I'd like to add some mid-fork bosses and a couple sets of rack bosses to the seatstays. Will the standard road bosses from Nova cycles (https://www.novacycles.com/catalog/pr...roducts_id=782) work on most early 80s lugged steel forks? Will I need to modify these bosses in order to ensure a snugger fit, or can I braze them as they are? Any advice on holding these things in place while I braze them? Thanks in advance.

if you could use the rack to hold it would be perfect. It doesn't take much to hold them though. I have seen modified spring clamps with a 1/8" brazing rod brazed to it uses as a holder.

You might consider using water bottle bosses instead of this, then you could use silver. Holding them is also quite a bit more trivial, i.e. nothing is required other than gravity

Normally the front fork braze-ons are done with a water bottle mount. They can also be done with the rear stay mount you show, though it looks uglier. If you are making your own racks you should be able to choose the position with some care. Start backwards. Choose panniers, design rack, modify frame to carry rack dead level.

When it comes to positioning the BOs, those spool shaped ones are normally mounted on a piece of threaded rod to keep them aligned with each other. If you use the water bottle mounts they are positioned in holes, though getting them square may take some fritzing. A rack is not always a perfect mounting jig, since even a well made rack is not always bylaterally simetrical. It's a back and forth process. You design the rack. You positon and install the BOs from the rack, then you install them, then you mount the eyelets to the inserts/BOs, then you braze the rack to those. Something like that. If you are going into production you build manufacturing fixtures so that everything is interchangeable, but the fun of custom is being able to tweak everything.

I have something similar in mind, but I plan on modifying a cetma rack to attach to bosses brazed into my fork crown. Is that a safe thing to do? will it weaken the fork too much? Its from a 1985 bridgestone T700.

should be ok, it's fairly common. I wouldn't add braze ons unless I was already painting a bike. P clamps look fine.