that was probably originally an 1850 bulb. (5v, 90ma) but anything in the 6 volt range should work okay...#755 etc.
heck, search ebay for some 5 or 6 volt LED bulbs with a "bayonet" style base also known as a "BA9S" size base and be done with it forever.
the #63 you've chosen will probably work alright. depending on the current going out to them from the harness they might be a tiny bit dimmer than the original. not enough that you'd notice. but it's better than burned out right?