There was no "1989 ban", per se. The changed that stopped the imports of rifles in certain configurations was merely a reinterpretation of "sporting purposes" from the 1968 GCA. It is questionable whether or not Bush Sr. issued a formal executive order to the ATF causing them to make this reinterpretation, informally told them to do so, or merely just let it happen. The "sporting purposes" thing has been reinterpreted several times since - to the point today where you can't import a rifle that accepts a mag > 10 rounds with a thumbhole stock (considered a "sporting" pistol grip, but a PG all the same now).
The only new legislation signed by Bush Sr. was 922(r) in Nov 1990, which said that you can't reconfigure an imported rifle to a configuration that is not importable. Otherwise, you could import, say, a MAK-90 with the thumbhole stock and bare muzzle and simply (and legally) replace the thumbhole with a real PG setup, thread the muzzle, etc once it was in-country.
As for the "1986 ban". The bill was titled the "Firearm Owner's Protection Act". It was intended to get rid of some of the more nasty bits of the 1968 GCA, among which was you needed an FFL to buy ammo across state lines. Also added some other protections, like allowing you to travel with a firearm from point A to point B w/o worrying about state/local laws in between, as long as it was legal at the start point and destination, made face-to-face interstate purchases of long guns with an FFL holder legal. It also had many protections added for dealers.
The "MG ban" was something the democrats added in at the 11th hour. Of course, it was sufficiently vague enough (just like "sporting purposes") that it could be interpreted different ways. The interpretation of the ATF, was, of course, to prohibit the manufacture of new MG's for civilian use. So... the congressional republicans as well as Reagan were basically damned if they did, damned if they didn't.
So, in summary, the "1989 ban" can't be repealed because it doesn't really exist. The legislation that needs to be changed is really the 1968 GCA.
Rocko