AA use Sabre so the record locator will be different than the Amadeus record locator which BA/IB use. The AAdvantage AAgent should be able to give you this. Once you have it you can use it to see your booking on www.checkmytrip.com and also assign seats on BA.com for your BA flights UNLESS the pre allocation limit has been reached in which case you're SOL as has happened to me despite being in J and the flight being 9 months away. The AAgent should give you a phone no. for IB to assign the seats over the phone. I don't know if this can be done online via www.iberia.com.

As for the best seats on a 747 search the BA forum but bear in mind some of the better seats are held back for BA Golds and/or till OLCI @ 24hrs pre flight time.