Jut found this older thread. Did you ever solve the problem? I had a similar issue recently trying to fit 1st-gen Dura-Ace levers onto Campag brazings. It was a no-go originally since early D-A, Arabesque/600 and even Golden Arrow/105 used a proprietary Shimano brazing for a fair old while. In the end Shimano switched to using the standard Campag style brazings around the mid 80s and stuff was interchangeable thereafter, at least for a while.
The main incompatibility arises because of the wedge-shaped parts that's part of the clamp band and which sticks forward. This is in fact the stop for the lever, and replaces the square washer with the tab that you get with Campag levers. You'll notice in the above pic that there's no square surround to mount such a washer in place, since it's not needed. This in turn means that you can't simply mount the Dura Ace levers on Campag braze-ons! I solved my issue by buying some NOS friction levers from the mid 80s and bodging various parts on place. As you might guess, I ended up with a slight issue with the size of the retaining bolt since it's rather loose in the brazing hole, but you can address this with some thin-ish cardboard to take up the slop. It's just a retaining bolt after all.
I don't have any issue with running my levers this way, so I wonder why you want to change it? Personally I'd put the levers back on this clamp and use it as intended - it's a pretty good design! If you really need to use a different band, then try looking for an Arabesque or Golden Arrow one from the same period, but you'll probably have to buy a set of levers. They come up often enough though. If you do go ahead and replace it then someone on here was looking for a one of these clamps last year, though they may be sorted now. I'd be interested in it if you still have the bolt?
Cheers,
Gareth.
