ACFT TAXIING; CALL SIGN MIX-UP BY GND CTLR CAUSED CONFLICT BTWN RPTR ACFT AND A WDB ACFT. RPT HAD TO SPD UP TAXI TO PREVENT A COLLISION.

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LANDED ON RWY 24R; EXITED ON THE REVERSE HIGH-SPD (TXWY Y) AND HELD SHORT OF RWY 24L AS INSTRUCTED BY THE TWR CTLR. CLRED TO CROSS RWY 24L AND INSTRUCTED TO CONTACT GND CTL. GND CTL ACKNOWLEDGED OUR CHK-IN AND TOLD US TO PROCEED E ON TXWY E. WE HAD OBSERVED A B747 HOLDING SHORT OF TXWY Y ON TXWY E EVER SINCE WE HELD SHORT OF RWY 24R ON TXWY Y AND CONTINUED OUR VIGILANCE AS WE PROCEEDED S ON TXWY Y TO JOIN TXWY E. WE EVEN HEARD GND CTL ADVISE ACR Z OF OUR CONVERGING TAXI RTE FROM HIS L SIDE. (NOTE: THERE IS NOT ENOUGH ROOM TO CLR RWY 24L ON TXWY Y AND HOLD SHORT OF TXWY E DUE TO THE ANGLES OF THE INTERSECTING TXWYS.) WE HAD PLENTY OF ROOM TO MANEUVER CLR OF RWY 24L AND ENTER TXWY E AND WE HAD THE APPROPRIATE CLRNC TO DO SO. EVERYTHING WAS NORMAL UNTIL THE B747 THAT HAD BEEN MOTIONLESS DURING THIS ENTIRE SCENARIO BEGAN TO AGGRESSIVELY MOVE FORWARD JUST AT THE MOMENT WHEN WE WERE AT THE MOST VULNERABLE POS TO CAUSE A CONFLICT. OUR POS WAS SUCH THAT I FELT AN EMER STOP WOULD QUITE POSSIBLY NOT BE CLR OF THE B747-400'S 213 FT LONG WING SPAN AND I ELECTED TO INCREASE TAXI SPD ENOUGH TO STAY IN FRONT OF THE B747; WHILE ANTICIPATING THAT THE TAXIING PLT WOULD LOOK DOWN FROM HIS PERCH AND SEE WHAT WAS GOING ON AND DISCONTINUE HIS MOVEMENT -- WHICH IS WHAT HAPPENED. IN THE EVENT THE 'ALUMINUM OVCST' CONTINUED MOVING; I FELT THAT I COULD HAVE INCREASED TAXI SPD ENOUGH TO STAY OUT OF THE WAY. TELECON WITH LAX GND CTL SUPVR CONFIRMED THAT WE DID NOTHING WRONG AND AN APOLOGY WAS GIVEN TO US FOR A MIX-UP IN CALL SIGNS. THE TAXIING B747-400 WAS ACR Y FLT XXX AND NOT ACR Z FLT XXX; AS WAS USED IN THE PREVIOUSLY MENTIONED ADVISORY GIVEN BY THE GND CTLR. ADDITIONALLY; NO REASON COULD BE GIVEN FOR THE MOVEMENT OF ACR Y.