The guy that wants to ship the 80% side plate didn't state whether he was a dealer or not. I assume he's not? If so, I would ship the sideplate, since there's probably no numbers or address on it. The guy building the gun would have to do this. As a dealer however, I would take a more cautious approach and probably insist on shipping only a 100% plate.
I was a Class 3 SOT for 28 years and for the last two years, I've changed over to a 07 Mfg. 02 SOT. I get yearly compliance cks. and have never had a problem. I do however know of dealers that have had problems with BATF and it's no picnic! Most of the ATF field agents don't have the least idea what a 1919A4 is let alone an 80% sideplate. They're more into dotting "I" s and crossing "T"s and bitching about paperwork errors. Their's a lot of paranoia about ATF Agents kicking in doors etc. They usually don't do this, but they sure as hell can if they "suspect" something might be afoul.
Dont misinterpetate my comments about ATF agents all being great guys. Some are definitley assholes, (just like the rest of us) and when I run into one of these, I don't take any of their bait! I agree with 30 cal. that the CA dude that wants the sideplate might have a bigger issue with the CA DOJ than BATFE.
CA. gets a bad rap on their gun laws, many of which I don't agree with, but I still sell firearms to CA. people. Yes it's a pain in the ass, jumping through the extra hoops that go into effect tomorrow thanks to the CA DOJ. However, the people that live there and have/buy guns are people with the same interest that I have. If I lived in the State of CA. I'd have at least a dozen 1919s and enough ammo to melt the barrels out of every damn one of them. They're gonna need em in the not so distant future.