Well I bought an Uphanger and it doesn't work with my fork
You need a lot of exposed fork crown like you get in most welded unicrown forks. An old style brazed fork like mine has about 14mm (vertical) of attatchment face on the crown then the lower headset race juts out.
Also the distance between the fork crown and the cable centreline is much smaller on my bike, I imagined that would be standard, silly me.
The only solution is to make my own (with an integral lamp mount and threaded adjuster) out of some aluminium stock. Gotta be the good stuff, failure of this part will not be pretty.