Being impatient (and poor), I ended up cutting the back out of the original sealed beam and fitted a 60/55 globe and holder.
Top it off with a 12V reg off an old 610 Husky and a switch block from an XT550 and I've now got lights!
And good lights too!
It did take while to get working though, cos the brand new fuse holder had an open circuit inside the moulded bit!
Thanks again for all the advice. I didn't follow any of it.........