So the takeaway is:

(1) DAL is a better bet than UAL with regard to the likelihood of getting offered a seat in business class.

(2) There is no special line or office to go to at JFK/EWR or LHR. Just make sure to get to the ticket counter 2+ hours early to get listed and pay the taxes.

I'll only be in London for a couple of days so I'll try to list for the return flight as soon as I arrive from NYC, if the lines aren't too long.

Thanks for the replies.

Tipsy