I don't know if you're still looking for your filter, but I just obtained a custom-made adapter allowing me to use the B+W 105mm filters on my big ol' 40mm Distagon. It cost me around $60 (Contact Martin Skoda at FotoSkoda in Prague : martin.skoda@fotoskoda.cz). I picked it up in person at their service desk and brought my lens along —which permitted them to made final adjustments—, so the adapter fits perfectly. I don't know if (and I doubt if) this is necessary with each lens, but ... just so ya know. Better to ask, I think. But the price is right and the precision, irreproachable.

Best,

Chris