SOLVED: How do I get this Syncros Cattlehead off my head tube/steerer tube?

[ishaw]

What was left as evidence of the cause of the stuck stem, out of interest?

 

[YoungOl’Timer]

The first rule of retro bike fettling is that you must get yourself a large mallet!

Noted.

 

[YoungOl’Timer]

What was left as evidence of the cause of the stuck stem, out of interest?

Looks like just a bit of bad manners and stubbornness, from what I can tell.