Oil confusion, please help!

[jmon1123]

Hey all, I recently got a ‘69 long step, from the forest service up in wahington.
I will try to post photos later, but onto my question. in it, is it’s factory 292 with the granny 4speed. I want to do an oil change and shang the sparks, but i’m confused on what oil to use. I’m seeing so many different claims saying you need this additive or that additive. I’m in oregon and the temperature is getting down to the low 50s. If anyone has a solid answer it would be greatly appreciated. Thanks!