I picked up one as well and even after flying to pick it up and fuel for driving 700 miles back I'm in it less than $4K. My theory was fleet maintenance to some extent mitigated the 330K miles and even if it takes a crate engine to keep it running I probably still get enough value to be worth it. Turns out I got 19 mpg on the drive back and the only thing I've found wrong with it so far is dead battery in a tps. Wrap is goofy looking but at least I'm never going to lose it in a parking lot.
When properly cared for, and owned outside of the rust belt, these vans will go a million miles. Hell, I've seen a Chevy Express van in the rust belt with over 500k (that's 800k if you're French).
They're so simplistic, and parts are so easy to find, that frame rot is really the only thing that can permanently kill one. It's really a shame that the Express is the last van of this breed that's still hanging around. The stubby nose makes spark plugs a harrowing experience, but everything else is easy. They were built to be used indefinitely.
Wouldn't even need a crate engine if it came to needing a replacement, a good used engine for that would be easy to find.