Recently I was given a vintage Lejeune frame to repair and modify. The owner wanted me to spread the rear dropouts to accept a 130mm hub, add water bottle braze-ons, repair the seat tube collar and remove the cable guides along the top tube.
Spreading rear dropouts of any frame is always the riskiest part, so that was the one I started first. Orignally the dropouts were at 123mm and the owner said he would be happy if I could get them to at least 127mm. After putting the frame in my alignment "table" I clamped the stays at chainstay bridge to ensure that when I spread them the bridge did not separate from the stays. Using the alignment table and my 130mm dummy axle I was able to ensure that the stays were evenly spread to a spacing of 127.56mm.
The next step was drilling four 1/4" holes in the frame for the water bottle braze-ons. On every frame I have build (with the exception of the track bikes) I have had to drill holes for the water bottle braze-ons. While spreading the dropouts may be the most potentialy destructive, drilling holes in the frame for the water bottle cages is definetely the most nerve racking. That said, these presented little to no problem and turned out pretty good.
Compared to adding bottle cage braze-ons, repairing the seat tube collar and removing the cable guides was a relative walk in the park. I had a threaded tube that accepted a M6 bolt that I used for the seat tube collar and the cable guides filed off without a problem.