Why not try finding the short harness sections for that kind of gauge illumination at the breakers? If the gauge has a metal back and hole for the bulb it's really easy, all you need is the bulb holder and few inches of wire to it from pretty much any 60s/ 70s BL car (run an earth if not already present, with a round terminal on one of the mounting studs).
Its worth getting the right part like Packedup and martylemoo have linked.
I had a bad experience with gauges. bought they off ebay, all bulbs were missing, some gauges didnt even work, with the response 'they worked Ok when I took them out'
I tried messing about with LED's for bulbs but the light output is directional, which was completely useless