Take one old style front bicycle headlamp bought from ebay for about £4. (this is a Halfords lamp, posher Raleigh etc ones will cost double+)
And one Cree torch of somekind bought from China of ebay. Mine is a 3xAAA powered 5W Zoomable Cree Headtorch which cost £5 posted.
Disassemble the Headtorch.
Go 'Ooooh' & 'Aaaah' at the tiny lens on the Cree LED. Decide whether or not you want to keep the larger glass lens & the zoomability. I decided against as the original lamps lens created a good light spread.
These are the only bits that we'll need from the Headtorch now. the LED unit has been de-soldered from the board to get it out of the casing. It will be resoldered later.
Discover that the LED unit and the Halfords lamp unit's reflector dish were made to measure for eachother.
Then discover that the headtorch's little on/off button is the exact fit for the original lamps red running light. - glue on/off switch in place. Remove rust/paint to your choosing.
Work out nice position for the battery pack and Alraldite in place. Work out some way of keeping batteries from falling out later - tape will do for now.
Put it all back together. Paint the bracket in Black Hammerite. & fit to the bike.
For other inspiration: Here's one made earlier by my brother using a Raleigh vintage lamp, painted with cream Rustoleum (Great stuff), a switch on top and using a Cree, powered by a large 18650 battery.