I can't remember seeing this particular article, but will have a look through the archives.
I have a Webley Senior .177 with extended barrel, with the extension measuring 6.5cm from the pivot mounting.
This just clears the trigger guard, and the only additional milling I can see is on the front face of the pivot lever, which has been skimmed by about 2mm.
There are a couple of pictures in the Webley Senior sub album on my sig site.