The standard 6v battery is group 1. 12v sizes are also shown.

6v and 12v bulbs

Most vendors sell fuel-gauge resistors (Runtz style). Some people say that this reducer is not Runtz-style but it has worked fine for me. Your resistor/capacitor might work or might not - do you have a breand and part number?

You have probably seen this article on the 10SI

Here is another article on the 10SI