Okay thinking of buying a MAC and the guy says it's preban. Serial # (lower) 89-0042xxx, preban? If so, he has a post ban upper on it, can I order and install a preban threaded barrel on it? If I was to get a tax stamp for a suppressor is it legal to install on a preban MAC-11? Sure this is a class 3 dealer question just wondered if anyone knew?

Personally, I wouldn't touch the M11 if it wasn't full-auto.  I had one in 94 and the thing was pure junk.  It would only be worth it if it could pump our 12rnds per sec or such.  Otherwise, I'd look to save the money for something better.

if this is one of those m-911's i wouldn't own one at all---had one years ago and something was alway breaking--if this thing has plastic mags like the one i had they are junk also....Dick

Yes this gun is preban. In the serial number the first two digits represent the year of manufacture, so this one was obviously made in 1989. Because this gun left the factory as a preban gun it is grandfathered and you can replace the postban upper with a preban if you would like.

It would also be completely legal to buy and attach a suppressor to this weapon, as long as the suppressor itself is registered.