I'd take it to someone who does rust work on these older cars and trucks and get him to look at it.
I've found it hard to find good and reasonable people to work on these boys because it's so much work.
If you don't care about the rust just run it until its not safe or fun to drive anymore. Who cares in a work truck.
If you want a good driver that looks good and you'll keep it then you'll probably have to tear this thing apart to get all the rust. I'll bet the caps are bad, I'd worry behind the bed on the cab, around the windshield, the rockers will be bad and I'd worry about the firewall. The pans aren't that hard. You can fix the bed easily. Replace the panels. They are cheap. So is the hood. In fact the parts are cheap. It's the labor and time to cut or remove things and reweld and replace. Then you gotta prep and paint it. It's probably rusted up around the front of the hood as well.
If the motor and drivetrain are good then it's a good deal for the parts. Run it until you find a good body and swap them out if it has a heater that works and doesn't leak.
If the motor needs rebuilding, the tranny needs work and the frame is so rusty stuff looks like it's going to fall off then stay away period.