This reminds me of a situation I was in about twenty years ago when I was rebuilding a mismatched but genuine 4T & scope combination. The fit of the bracket on the pads was ok in the vertical plane but well off laterally. I liaised with Peter at the time, & as usual his comments were of great help. I ended up removing the rear pad & soldering it back on several times, each time surface grinding a thou or so off the rear face, until it was just so. It was a complete & utter pig of a job, & I'll always remember what Peter said afterwards - something along the lines of 'Good! I'm glad it was a baXXXrd because you've learnt a lot from it & now more fully understand the importance of getting it right' (well, there was probably a few expletives scattered in there as well!).