Methinks that's mostly nonsense. Assuming it's a vintage later than when Calif began requiring more stringent emissions equipment (e.g., PAIR system, cat. converter and/or charcoal canister) than the other 49 states, then the only real issue is whether it has 7,500 miles or more on it. If it does, no problem.
My FJR is a 49 states model, bought new while I was living in Nevada. When I came back to Calif, it had over 7,500 miles on it and it was no problem to register (a half hour?). Same thing with the '03 Honda Blackbird I bought used while in Nevada and returned with. The only extra requirement was that I had to take both to the DMV office where an agent checked my engine nos. on cases, SNs on the frames, and checked to see that the bikes had the emissions stickers required in the state of origin (i.e., the 49 state model EPA stickers). It helps to locate all those numbers before the trip to the DMV, so you can assist the agent in finding them.
If anything, I'd expect vintage bikes to have even fewer problems, not least because back in the day, no one was making 49 state and Cali versions of the same models.
Have him do the research, put the responsibility for any issues with registration on him, don't let your bike head across the country without money in hand and a signed bill of sale that specifically delineates who has what rights and responsibilities once it ships or is delivered to him or his agent. I'd beware anyone who wants to make unspecified registration "requirements" your problem unless it's just laziness and ignorance on his part. So I think I'd ask him to lay out, in writing, exactly what is required with citations to the California Vehicle Code. If there is a specific issue raised re: your bike, then at least it's addressable, but the general whine doesn't provide anything useful.
GLWS
