The light unit arrived a couple of days ago.
I went for this light unit as the shell has more flat area for the mount than some others.
The back is aluminium but the lens is a flimsy feeling bit of plastic.
You can deform it with finger pressure. I think I will get a tablet screen protector for it.
I cut the three mounts off an old lamp and drilled mounting holes in them for the screws.
Attached the mounts to the adjuster post and the pivot point on the headlight frame and positioned it on the new lamp, making sure it was all square.
I marked the drilling points with a fine tippex pen and drilled a tapping size hole. (carefully!) in the shell.
I used 3.5 screws, 9.5mm long. I did puncture through the shell, but "only just", which is why I put blobs of polymer adhesive on/around the holes before putting the screws in to keep it all watertight and give a bit of extra hold.
Fitted new pivot bushes and attached the frame.
I cut the beak/visor off the old unit and glued it onto the new unit.
Waiting for the jibber to dry now, before reconnecting all the wiring and fitting it into the bike to see if its all aok.