Are you trying make it look original with 'LUCAS' moulded in the glass ?
If so, what will a repro Fergie glass have on it ?
If not looking for originality, 7" headlamps are readily available but be careful buying from Ebay.
I purchased 7" Ebay headlamps complete with globes. The globes were rubbish and 'horizontal' lines on the glass sat at odd angles where the glass had been misaligned during manufacture.
I threw them away and purchased lamps from a local Narva supplier. Look OK, work perfectly, just don't have LUCAS on the glass.
I did try to remove the LUCAS glass from an old light unsuccessfully. My thinking was to bond the old glass to a new bowl.....I will try again sometime.
Colin

