Pryso, Dennesen sold a separate device for dealers. I couldn't remember the name. I searched for a photo, but couldn't find one. It was called the Pivotram and used for locating arm mount holes. I do the same thing as you - reverse the SoundTractor bar and use a ruler to measure distance. It's easy for me to correct for the offset of the bar and get a pretty accurate mount hole. There is usually a little play in the fit of the arm pillar into the hole, especially with DIY drilling.
When using a pivot pointer device like this to align, it doesn't matter if your mounting distance is off a hair or two, as long as you can align to the grid with the pointer in correct position, your alignment is good. A SoundTractor or Feikert works where the pivot is actually located, not where it theoretically should be. If your arm mounting distance is off a bit , and you get a good alignment, then your offset angle will also be off a hair. Here's an old discussion about it. My user name was lfleib.
http://www.vinylengine.com/turntable_forum/viewtopic.php?t=10827
With most pivoting arms the cantilever is not pointing to a pivot, due to offset. The discussion of maintaining mfg. offset is arm specific, and should be limited to that IMO.
RE: the quote - I tend to think the Brits should be blamed for most things, but I don't know about the Japanese use of the Stevenson alignment. That seems a bit of a stretch. The use of Stevenson was a very sensible thing at the time, but became a sort of default standard along with 15mm overhang. If you have an arm designed for Stevenson, there are some options.
Part of the quote was linking Dynavector to Stevenson. It is not.
Regards,