You should begin sourcing a ballast resistor, an externally resisted coil and a starter switch with side terminal. The internally resisted coil method is not for our trucks. It is the wrong method. None of this is original to your year but the external R method is original to what was used when Chevy went to 12V.
Here are the parts, or an equivalent, you need:
Ballast ResistorStarter switch CoilI will explain wiring these after you get them. You do not have to buy them, you can use what you have but there may be issues at some time. You can wait until the money is available or issues show up. (hard starting, points burning out, coil failure)
