Indeed; since departing from T3 , you cannot use the BA lounges
Are you connecting in London or actually stopping. If connecting, it would seem madness to me to put a LHR-LGW connection in just for the sake of lounge access; if you really want lounge access in that instance, just switch to BA LHR-LAX and have a nice easy connection T1-T1
If you are stopping in London, then I would switch to the LGW departure
As far as searching for small words, google will do it ; put the seach criteria in plus site:flyertalk.com
Dave