Hin dfearns,
The 747-400(1) is the LGW base aircraft with fewer Upper class seats and more Economy seats ( also the Nova entertainment system)
The 747-400(2) is the LHR equipped fleet ( your flight to SFO) and has more Upper class seats ( the J2000 with the bar on board)
This fleet has either vport, Arcadia or Odessy entertainment systems ( more choice than Nova).
The service on board is the same.
Have fun
Regards
TBS