I have been on the search for a 1st generation K5 for a year or so now. They are definitely getting rare. Rust-free is even more rare.
I myself wouldn't be too worried about the drivetrain as much as I would be about rust. Is there rust anywhere? rockers, floor, bed floor behind wheel wells, etc...
Windshields sometime have an issue with rust, as well as the rear hatch on the hard tops.
-Does it have A/C, or did it at one time? Or was it a non-AC truck from the factory?
-Is it a 4wd model or 2wd? The 2wd are actually bringing more money even though I think they are horribly ugly with the top off.
Post up some pics...the 69-70 grills are my favorite compared to the 71-72.
Keegan - 913-991-8478