That is a pretty impressive build there but I’m at a loss as to what you can do with it without scrapping the whole design. Bulb holder and all looks built in to the battery holder and I’m clue,DSS how you could modify it with an led driver and modern led. 5ats a head scratcher right there. If I were you I’d leave that one of a kind as is and get a new mag to mod or explore the option of getting a new, modern light that already has what you want.