Just to beclear about it, the Magnequest upgrade parts BH-1 and BH-2 fit mechanically and electrically, in any version of the Stereo SEX amp. The new Bottlehead parts OT-2 and PC-3 also fit, and have similar specs to the Magnequest parts. There is an audible difference between these two sets of iron, but it is small and more a matter of taste.
The old Stereo SEX amp (variously called version 1, 1.0, 2, or 2.0) was in production from 2004 to 2012, and that version benefits (especially in terms of bass power capability) from an upgrade to either the Magnequest or Bottlehead parts mentioned above.
The current Stereo SEX amp, V2.1 on the manual cover page, incorporates the OT-2 and PC-3.
Incidentally, I have started a new thread on the version names, because we have been a little sloppy about it over the years. :^)