First '78. What should I do?

[oneday1]

Hey all. First off, want to say I've been reading the forums and am loving all the info available here. Great site...keep it up!
So, I recently decided to purchase a truck for work and was looking through the classifieds when I found this one. 1978 C1500 Heavy Half. Fell in love right away. Paid 1500 for it and am not too unhappy with the price. It has very minimal rust and body and frame seem straight and solid. It has a number of small issues such as gas gauge working erratically (locking in 3oclock position sometimes) fuel tank switch doesn't work, slight oil leak, etc. I was just hoping to see if anyone had any suggestions, concerns, or things to watch out for or take care of right away to keep the truck healthy. I'm mechanically able and was a diesel mechanic in the Army but honestly have absolutely no experience with older gas trucks. Any help or pearls of wisdom are greatly appreciated. Thanks.