I can't find it right away bit there is at least one post (with photo) of a bracket made by Barry Churcher that fit between the original mount and a master cylinder similar to that mentioned by GJamo.
If you can find an original (even one that is pitted so that it is unusable) consider getting it sleeved with either stainless steel or brass. Many people have reported success (only a few report leakage between the sleeve and the original metal).
On edit, this
http://www.mapleleafup.net/forums/sh...ghlight=master is not the thread I was thinking of but is another approach Barry has used...