Lynnmor has a good idea IF you can find a better radiator for the 1/2 ton chassis. A bit involved unless you find a HD version made for that setup, but first check/ replace all the easy stuff.
The van is low miles and should have a lot of life left in it, but I'd be wary of towing much over about 6,000 lbs and even then, take it easy on the van. Had a couple efi 302 pickups of that era and they were super solid, but not something I'd want to head X country towing a heavy trailer with.
Good luck with your repairs and the best to both of you.