This thread makes me happy for a couple reasons... Not only did you decide to keep your fathers truck and get it back on the road, but you're also going about figuring the truck out right. Too many times do new people come around and just want to be spoon fed information instead taking it upon themselves to learn.
You might know next to nothing about Datsuns (and even cars in general), but you were smart enough to look for a tech manual to help out. Z-Train hit the nail on the head about Chilton/Haynes books. There's some good info in there, but FSMs are where it's at. What I would recommend doing since you know next to nothing about cars would be to hop on Google or Wikipedia and look up the general basics of how each system and component work. It will help out immensely in your troubleshooting and maintenance.
Welcome to Ratsun, welcome to Datsuns, and welcome to cars. Good luck.