1600 sounds like a lot for any 85 unless it is really special. Most engines are pretty worn out by 450K but it might not be and might not be original either. Adrianspeeder is right about other things that might need help that could get expensive. This is less of a problem if you can do these repairs yourself, but it should still be reflected as a decrease in the sale price. Some things I'd be worried about would be radius arm bushings, kingpins or balljoints, the axles themselves, and the entire drivetrain. I'd also have some concern if the truck was from a place close to the ocean and or where salt is used on the roads. These kind of repairs can get really expensive. Maybe he's already had some of this stuff replaced and is trying to recoup some of the money, if so he'd better be willing to prove it with receipts and subject it to your or a mechanic of your choice's inspection. As fr as the engne if it starts cold, has good oil pressure and not too much blowby, check the head gaskets and for any odd popping sounds through the exhaust or intake, otherwise it's probably good. The info is incomplete, but for that high of a mileage truck, I'd want to prove it was good rather than take someone's word for it or take a risk but buy it cheap.
