Again... Id rebrowse a few links I posted for AZ ones. If youre going carb engine.
Im not fan of those “classic car” sales places. They always have shiny paint. If youre spending that kind of money. Id make the time to drive or have someone you know drive it. Hell , maybe CK5 member is close by the vehicle.
Also for 15-21k you could easily buy a cheaper nicer truck and LS swap for under the 15k youre asking.
You seem to like shiny paint and have the $ to spend. So, ultimately, its you're choice. The 78’ I linked earlier is far nicer and half the price.
These classic car places are always more money than a private seller. They have overhead, employees and on and on.
Far cheaper and to me, better. But I prefer the round eye era trucks:
https://phoenix.craigslist.org/evl/cto/d/willcox-1979-chevrolet-k5-blazer/7063661916.html
Where are you located?