Since it is illegal to remove a VIN tag, the body, which is what the VIN tag is attached to, would be an '84. CA does not allow anything older than the model year engine to be installed. If you install a new year, you must have it approved by a CARB referee and it would be titled as the newer year of the engine, which has to have all of the original parts (cats, smog stuff, evap fuel containers, etc., etc.).[/QUOTE
Not now but they used too back in 1984. I worked for a guy in Napa that had a 84 S-10 with a crazy V8 from a 69 Nova. He bought the S-10 brand new and put the V8 in it within a few weeks. Back then as long as the engine had the smog equipment it came with it was legal to swap in a newer vehicle, all a 69 Nova had was a PCV valve. He said the CARB couldn't do anything about it now because it was a legal engine swap when he did it and he had documentation by CARB saying so.
So this van could be smog legal but do your research first. It's the sellers legal responsibility to smog the vehicle too. I used to have my CA smog license until I moved north.