We're getting off track. The OP asked what it was like pre-86 re NFA items. Well I've been around a while so let me chime in. Way back when the dinosaurs roamed the earth you could order Thompsons from several companies, by mail, that had been "deactivated" by pouring lead into the chambers. Later they actually tack welded a rod in the chamber. but they could still be freely purchased. Dewats and deactivated machine guns were not registered at all.
I can recall openly buying machine guns at gun shows in the early 60's. No one really seemed to care, at least in my area. They may have been under the table but they were sure there, and cheap. I can recall buying a .50 M2HB for $350 at one show in 1965 and I registered this gun during the 68 amnesty. I subsequently sold it and now I sure wish I had held on to it.
Parts to convert M1 carbines to M2 were easily purchased and they were cheap. Most MG parts were very cheap and easily obtainable. There didn't seem to be a whole lot of interest in them at that time probably because most prople didn't have the disposable income to buy ammo for them even though the ammo was pretty cheap. I bought two pallet loads of .50 BMG ammo from Ed Agramonte in NYC for .10 a round, new in spam cans, a mix of AP, API, tracer, APIT, and ball. I remember buying .30-06 belted ammo for as little as 2 cents a round because it was in belts and no one wanted to unlink it. I happened to have a handy, speedy delinker.
Ah, those were the days. We'll never see the likes of them again.
After 68 up until 86, interest increased in NFA items. It was possible to locate an old war trophy that hadn't been registered, take it to a manufacturer, and get it papered. That put quite a lot of guns into the registry, and I suspect that if BATFE opened up the registry again for either another amnesty or simply allowed someone to register previously unregistered guns, a heck of a lot more guns would come out of closets. But again, I don't expect that to happen any time soon.
Thanks for the question which allowed me to wander down memory lane again. It was fun.