On the single taillight question, the standard Chevrolet pickups typically came with one light on the left side, like yours. The Chevys also only came with a left side sun visor. That being said, some states may have required a light on both sides, on trucks registered in that state. I would guess that yours came with only one, if there is no indication of one on the right. Once the truck left the dealer, it's anybody's guess what was installed on it. I know it's fun to learn as much as possible about our individual vehicles, but without a sales agreement, or reciepts for dealer installed items, you really just do not know.
Because I'm still learning here about forum etiquette I may have lost some of you started a new thread "What am I doing " and just want to let you know that though the forum instructor hasn't smacked my hand with a ruler I was post the progress there. Please feel free to educate and discipline me as necessary
If you are starting a new thread, it would be appreciated if you would post a link to the new thread on here, although I don't understand why you would change threads.
Here is the new thread a continuation of this one. https://www.jalopyjournal.com/forum/threads/what-am-i-doing.1176475/
A suggestion..reference in your title the year, model, and that it's a build thread. Stick to that particular on going thread, adding new material as you go. People use the search thread tool, and in so doing will be able to find it and add/gather/input information about your build.
Because VIN numbers were not standardized until the 80s. Most online readers are wanting 17 digits for that system, but your old Ford just used a serial number. Some identifying info can be decoded using that. Just going to have to search for your specific application.