X2 on what Butch said. They are NOT idiots. I have imported several original Listers and they knew exactly what they were. The first one I imported one of the officers specifically asked the country of origin. Because it was coming from the UK it was clear but he did tell me that they were stopping a lot of the engines/machinery coming from India and China. I used my local port which is very small and even they knew what they were. Mine were completely legal because of their antique status unlike a 'roid. Remember Customs has access to google just like everyone else.
I had dotted all of the Is and crossed all of the Ts on my paperwork which made Customs easy and pleasant to deal with. They all seemed to take their job very seriously which I completely respect and appreciate. Their obvious focus is on drugs and intellectual property/counterfeit prevention but they do inspect everything and know what it is.
It is the freight carriers and bonding providers that are lazy gangster wannabes, not CBP. Those guys have their hand out at every passing and fleece you for everything they can every chance they get. I didn't have to pay CBP a dime nor did I have to pay any duties, the freight and import companies on the other hand, let's just say it was no small sum.