I'd also recommend going to the Pier F lounge (which is by gate 63) first for dinner/drinks/massage then head down to the QF lounge to wait for boarding. The Pier is an absolutely amazing lounge and in my opinion (and out of the lounges I've visited) the second best oneworld lounge after the QF SYD Flounge.
It is quite a long walk from gate 63 (where the Pier is) to where the BA flights usually depart from and the transit system won't be available as departing passengers can only travel in the opposite direction.