The "'89 Import Ban" really was just a change to the rules of the GCA68 for imported guns.  It changed the "sporting" definition to ban the import of semi-auto guns with "military features," such as:

- pistol grips
- bayonet lugs
- flash suppressors
- folding/collapsable stocks
- military bipods

For the purpose of THIS law, BATF ruled that thumbhole stocks were "sporting", so Uzis and AKs had thumbholes slapped on them and other offending features removed and were thusly imported.  These were guns that were still 100% imported parts, BTW.

Under Klinton, the importing of receivers, and later barrels, for "assault weapons" was banned by treaty or executive order.  Thus the "kit guns" began to show up, which, though largely made up of imported parts, had enough US-made parts to be considered "domestic."

Note: under the 94 Krime Bill, which covers both imports and domestics, BATF ruled that a thumbhole stock is still a pistol grip.  No more Uzis and MAK-90s.

-Troy