As above.
I think it came about when they started getting mounted in the ends of tri/TT aero extensions. Maybe for ergonomics, but it might also have just been done to look better when there is no rider on the bike.. Looks don't matter when your hands are cupped over them though.
There is a fourth type which typically is what you find on an aluminium frame and that is a welded on lump with 3 holes and the counterbore for a shouldered boss
Those bosses with a shoulder are meant for frames that have a counterbore in whatever is mounted on the forks or stays. The shoulder goes into that counterbore if you get my drift. Maybe removing the shoulder using a file/grinder/sanding wheel will allow it to work.
As a rule i am not into tall bikes, but this one i am. It has a steampunk vibe and looks alot better than the usual pile of bits in a shape of a tall bicycle.
What would be really nice is an organisation that puts in the same amount of effort , as some of you chaps do, into the riders that are also on the vintage side. I would also like some new joints, some filler in a few dents, a re-paint, and so on.
The frame for 513 notes will be available for a VERY long time at that price. Sadly; in todays depressed market, what you have is not worth a huge amount. Sad times as they are good frames and there are some good bits on it 😒
I have officially given up trying to find the seatpost.
It really is a bizarre thing and would love to know the story behind it. Was it even a real item? Was it put in for laughs like a dig at someone/a rival, or an inside joke? or slipped in under the noses of management who don't check...