the existing lamps are probably 47, 44 and/or 55's (ordered from dimmest to brightest and hottest). Some games also used larger #63's.
All are 6V bayonet style lamps - the 63 is a bigger one. Originally the machines typically used 44 and 55's, depending on lamp location. 63's were sometimes used to light large areas like the "play 1-3 ..." box above the coin entry chute on your game.
the pinball guys usually source from cometpinball.com or cointaker.com, and what you choose depends on how bright you want the game to be.
you always want a frosted 44/47 bayonet style lamp, and might as well pay the cost difference for non-ghosting so you aren't likely to get some dim illumination when the lamp should be off.
your options then are retro, 1SMD, 2SMD, and color temperature. Most common choice for color temp is warm white. Retro is close to a 44 lamp, 1 SMD is 1.5x brighter, 2 SMD is 2.5x brighter.
see
https://www.cometpinball.com/pages/the-art-of-pinball-leds