http://picasaweb.google.com/vernonlevy/Gate/

Another verbal attempt is that the mounts are best described as square
pads machined at their rears to accommodate the curvature of the
downtube. There doesn't appear to be any evidence of the blocks/pads
being sawn down. The bike was almost certainly a friction shift
machine - I can live with that.

If it's any help, the Frankenstein Fixed had band on levers. The
'mounting' is simply a tringular thingy with the flat bit towards the bars.
It's job was to simply stop the band on shifters from migrating down the
downtube. I'm wondering if your thingies are similar.