My van is also a 3/4 ton on 15 in wheels. Finding good load rated tires can be tough, but they are there. My van is bigger and heavier than this one by far and I still get my with the tires just fine. You should be OK doing so with this one.
I dont see much in the van; a bench seat that converts to bed, and the basic cabinetry. If the fridge works that is great. Sink is there but I see no tanks under the van, plumbing, or electrical hookups. This is not a Class-B where tanks and hookups exist, keep that in mind. Seems pretty basic and the price may be about right if the mechanics of the motor is sound. The Chevy 350 has been in use since the 60's and is a great motor.
The A/C is useless and dead weight. Unless the rig has a 30amp hookup, which I do not see one, and you pay for an RV park space, you will not be using it. You would be better off taking it off and replacing it with a 12v fan... unless you will be staying in an RV park mostly.
Talk him down under $5000 and I think you are in the ballpark.