First, welcome to the board and cool that you're doing a project for your son. Is he helping or a surprise?
pictures of the truck, a description of the condition, and the intended usage/how you want it to look in the end will help here
Until we have more details I always recommend getting the brakes in order. Then the electrical (checking for good grounds and no loose wires. Check for old rubber hoses or glass elements for the fuel supply, then get it mechanically running good. Then tackle the bodywork/rust repairs.
If it's a frame off restoration planned....start tearing it apart but save all the bolts in itemized bags and take lots of pictures because it'll make it easier to put back together....and plus, we all like pictures here
