I think it would be a great platform to start a project on. Old GM G-vans are great vehicles. If you don’t go after this rig PM me with the details as I may be interested. I assume the van is located in GJ area?
It most likely has a 350 engine, TH350 trans(maybe even a TH400 trans), NP205 transfercase with a Dana 44 front axle as most of the older 4x4 G- vans conversions where equipped this way.
On a 35 year old vehicle mileage is a mute point, as you might as well plan on a lot of parts replacement and updating. Adding an overdrive transmission and a modern fuel injected engine would be the first upgrades I would make.