Ok. let me wade in here.
THere are 2 laws that must be considered:
In '89 there was a "ban" on IMPORTING rifles ruled "nonsporting" - read military semi autos that looked mean. Eg., AK's Fal's, H&K's.
These FORIEGN made rifles were not allowed to be imported in there standard form - get rid of the EVIL features - pistol grips, folding stocks, flash hiders, etc. and they were considered "SPORTING". So foreign rilfes had to meet this new requirement to get imported.
IF
The rifle had enough US made parts, it was considered a US made rifle and could have EVIL features since it was no longer a foreign made gun. That is until '94 when the AWB was passed.
In effect, while your rifle was made before the ban. It is a nonimportable rifle in its current configuration unless you used enough US made parts to get around the Foriegn make requirement.
And yes others that tried the same have been prosecuted by the feds for assembling and selling "nonimportable" firearms.
Hope that helps.