OK, job done!
I resisted the temptation to bodge it by hacking the lead around at the back; figured I might as well get used to taking the front off, which I hadn't done before. Took a bit of fiddling to re-align the headlamp unit correctly when putting it back together. I know you have to be quite careful with the shear bolts on the mirrors, can't force them into position if not lined up right.
At least I know now that it's do-able at the side of the road, if necessary.
It's only 3 allen keys, after all.
Coffee break now!:P