Chombi1 

One thing to watch out for is the thread pitch for the mounting bolts are different between the Retros sold with a clamp and ones that were sold as direct bolt ons to brazed on shifter bosses. The pivot barrels on the clamped on sets are also larger diameter, but strangely, you can actually still remove the levers from a clamped on sets on to brazed on bosses and they will still work as the mounting bolts will adequately do the job to center and retain them on to brazed on pivot bosses. I actually have this going on with one of my bikes.
I currently have Retros on 5 of my 9 rolling bikes and have 2 spare sets in my stash and they do have a slight bit of differences between them in terms of feel and fit tolerance, but they all work great otherwise.