I bought my '97 a tad over 3 yrs ago, w/ 139k. Been a great truck.
How much are they asking for them? You can go to
www.kbb.com or
www.nadaguides.com to get an idea on price. Can also check
www.autotrader.com to look at the asking prices in those ads.
Biggest thing on a 24v, is to check the fuel pressure from the lift pump. It is goes out, the fuel injection pump (VP-44) isn't to far behind. The VP-44 is cooled and lubed by the fuel only, not by engine oil like the P-7100 pumps on the 2nd gen 12v engines.
PSI should be around 15psi at idle, and preferably no less than 8psi at WOT.
Those '99s may, or may not have to newer timing case. If they don't, then the dowel pin should be checked. Had to tap mine back into place.
Check the front end (steering) over good, to see if it needing attention.
If auto transmission, then make sure the oil isn't burnt.