Thanks both for the welcomes btw. Very much appreciated!

Info on seating seems pretty thin on the ground in that thread so I went ahead and did a booking on BA for AA/AA (which I then refunded straight away - still need to figure out exact dates).

Looks like my experience matches this post (29912029-post132.html) where I was indeed able to select MCE and "Reserved for elite" seats on AA website even though the website was saying in big bold letters that I had no luggage and no seat selection available.

Looks like that's what I'll be doing for my main booking as well. Thank you both again!