How many miles are on it?
Since it's not going to be a daily driver, you won't have to be under the thing all the time with the stress of needing to get somewhere. That's a good thing.
First thing I would do is check the plugs and oil to see what condition they are in. Climb up under it and look for oil leaks - also check for a leak in the power steering pump (that's a common problem) and the transmission and transfer case.
Ask the owner about oil consumption, oil change intervals and service intervals. Look at the tires for unusual wear. Climb up under it and knock on the frame and look for rust everywhere. Also check the condition of the exhaust system, and make sure the cat looks good.
If you can take it a little further than that, do a vac test on the intake manifold - there's a good tech write up here somewhere about what to look for, I think. Also do a compression test - wet and dry - very important. If you can't do any of these, pay a mechanic $50 to go over it - that's cheaper than finding out you've got a $3k engine rebuild in 6 weeks.
If you plan on keeping it tagged and inspected, and if you have to have a smog test done in your area, have it put on a exhaust gas analyzer and see what comes up. A competent tech should be able to tell you what the readings mean. If things are afoul, and it won't pass a smog test, don't mess with it. If you don't have smog testing, still take it in for the same thing and see what the results are. If the HCs and CO is crazy high, that means there's a mechanical problem you're going to need to work out right away. High numbers on the Nox can mean a bad cat or EGR problems.
Run a carfax report on it, too. If it's ever failed a smog test, it'll show up in the report (not everything does, though, like wrecks, etc...)
Here's the thing - I'm a 60 owner. I love my truck, honestly, but it's not for everyone. The ride is ROUGH. There's a ton of work that you have to do to these things. Sure, they keep running and running (mine has 205k on it) but you have to work on them to keep them going. You buy a 60 because you love it, and you want to take care of it, and because you're not afraid to work on it. Things are breaking on the 60s now because of the high mileage/age, and it's not stuff you can run up to NAPA and grab a lot of the time. (It's taken me 5 trips and a good deal of time to get the right pulley and belt for my alternator - putting the third belt on it tonight and I hope it fits...) - and the parts are not cheap.
Think hard about it. You may honestly be happier with cool toys for your 80, and the time spent working on the 60 might be better spent on your 80.