[Cool Hand Lurker]

Get a copy of the Model A Owners Manual and carry it with the car. Show the number-checking person this page where it says that the engine number is the serial number of the car. Don't agree to pull the body so the frame number can be observed without a fight.
And make sure the SN (Serial Number) that is on the title (if you have one) is the same SN that is on the engine. If the engine is blank then stamp the title number on the engine. Don't worry about the scare tactics in California. As soon as The Wall is built it will go around the eastern and northern borders of California and that state will then be part of Mexico anyway.