SEM Trim Black is right on the money as was suggested, and so is Wimbledon White or Ivory. I've done restoration for over 4 decades and found lots of ways to make the process smooth and easy on many things. Also, ways to make the part look like OEM when it's done. Taping is fine for some, but do we think the "General" had folks on the line or in supplier shops taping that part? NFW as in "NO (fill in the blank) WAY". It was sprayed and wiped off where it wasn't wanted and most likely a 1pc mask covered the already painted letters. Now in order to make it a painless and authentic process you need to get the idea that less is more established in your psyche before you begin.
You mentioned primer too, and SEM also comes to the rescue with black Self-Etching primer. Now here's where less is more. You want 1 light coat of the primer on both sides of the fin (or in the "valleys"). Within 10-20min, not much more, take a smooth fine rag, even something synthetic, and wet it with solvent. DON'T SOAK IT, just wet. With a suitable backer (as suggested a sanding block works) gently wipe the tops of the fins. You won't get it all in 1 pass so don't try, but after a couple passes change the rag to a clean spot. Only take off what comes off easy, and there's sure to be remanants left behind on the fins. Once you've solvent wiped it and it's all dried up take a conventional soft rag on your finger tip and remove the remanant "film". It comes right off easy and leaves clean chrome behind. Do the same with the SEM Trim Black and you'll have what looks like NOS. Now here's where the fun begins. You want to make a paper mask around the letters. That's where taking your time and enjoying the work comes in. Lay the paper on the letter and scrub a pencil over each one. Cut em out with an exacto knife and it's better to be just a wee bit tight vs loose. The spray technique works on the letters too. Excess material will not only look all buggered but can make the detail/clean up process look like poop. Light easy coats rule the day and look like a GM part when done. Good luck, and show it off when it's done.