I've owned literally dozens of G-Series Chevys over the years... If I could find an '86 up here in that condition I would love to have it. The "rust" your seeing underneath is MINIMAL. While considered "unibody", all of those frame components are far thicker than any typical unibody car. I think the underbody looks great for its age, and thats why he did take photos of it. Take it home, pressure wash the bottom, then soak the rascal up with Fluid-Film. It will soak into all the nooks and crannies and give that nice old van another 30 years on the road.
Parts are easily found, dead cheap and reliable. The only G-series van I've ever hated was the one straight six powered one and the V-6 powered one. Way too little of an engine, and the mileage wasn't a stitch better. They have all been 16mpg max vans except in the mountains.
This particular one may or not be fuel injected..... for my use, I'd hope NOT because first of all, these vans did not get ANY better mileage injected (more power yes, but not mpg's), and second, any fuel injection system related failures always cost an arm and a leg these days whereas a good Quadrajet rebuild and a mechanical pump replacement will be under $150. Easy to work on too !