Both blocks were about the same distance from the rim - about 4mm further than they should have been! If I could angle the fittings in a little I would probably have got away with it but, as I said, that moves the brake block up as well as in which would put it into the tyre.
So, I'm left with three choices - Use a wider rim (Mavic 281 for example), buy the Magura braze-on fitting kit , remove the U brake bosses and fit that instead or go back to a U brake (or a roller cam).
Normally I would just go for the braze-on option (at about £20) and get my brazing gear out, but for some reason I'm rather loathe to irreversibly alter my old friend of 19 years and I'd never match the paint job
I think that it will have to be a search for the ultimate U brake - I'm sure I can find something quite tasty...
Simon, again many thanks for all your input - as for the Maguras, I might be able to persuade a friend of mine that he "really needs" them. If not, there's always the "For Sale" section here (or eBay of course...)
Or I have a Kilauea out in Greece that might like them - loads of options
