I'm not saying your wrong, but something doesn't sound right about that. Was it DMV that told him that or DEQ? When I was in Tucson in the late 1990s, some of the DEQ inspectors were real zealots and would argue or try to fail cars with engine swaps. They will tell you it is "altering" emissions equipment. However, they should of made him, if missing or altered, correct the engine for emissions equipment for the year of the block. If putting a Big Block motor into a car that only came with a small block, then any small block should of been fine, not just one from that year model.
A 350 ci chevy engine is a 350 ci chevy engine. Main differences between some were whether they had 2 bolt or 4 bolt mains, iron block or aluminum. The numbers on the 454 I bought, that series of motors were put in cars, trucks and motorhomes. Someplace like Cali, and maybe Nev, I've never lived there, might say something if you put a Big Block into a car that didn't have that option for that year. The extra weight would affect handling, breaking, safety, lots of things. Big Block was an engine option on the car I'm working on.