A B767 WAS DISPATCHED WITH B757-200 SOFTWARE LOADED IN BOTH EICAS COMPUTERS. SIT OCCURRED WHEN L EICAS COMPUTER WAS REPLACED.

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WAS SENT OUT TO WORK AN 'EICAS DISAGREE' MSG ON LOWER EICAS DISPLAY ON ACFT X. MESSAGE WOULD CLEAR; ONLY TO RECUR SHORTLY. DISAGREE CODE WAS; '#2 ENG EGT.' NOTED 15 DEG SPLIT BETWEEN L EICAS #2 ENG EGT READOUT AND R EICAS #2 ENG EGT READOUT DURING ENG RUN AT GATE. REPLACED L EICAS COMPUTER; CROSS LOADED SOFTWARE FROM L EICAS COMPUTER TO R EICAS COMPUTER. RAN #2 ENG AGAIN AND L AND R EICAS COMPUTER BOTH READ THE SAME. #2 ENG EGT AND 'EICAS DISAGREE' MESSAGE WAS NO LONGER PRESENT. SIGNED LOGBOOK; DISPATCHED ACFT. FOUND OUT LATER THAT I HAD CROSS LOADED THE EICAS COMPUTER SOFTWARE THE WRONG WAY. THE L (NEW) EICAS COMPUTER THAT I INSTALLED HAD B757 SOFTWARE IN ITS MEMORY. WHEN I CROSS LOADED FROM L TO R; I INADVERTENTLY INSTALLED B757 SOFTWARE INTO BOTH COMPUTERS THAT WERE IN A B767 ACFT. THERE WAS A CARD ATTACHED TO THE NEW COMPUTER FROM STOCK DENOTING THE SOFTWARE VERSION; BUT NOT DESIGNATING THE INSTALLED PROGRAM AS BEING B757 SOFTWARE. THE COMPUTERS IN THE STOCKROOM SHOULD HAVE A LABEL ATTACHED OVER AT THE SHOP DENOTING WHICH ACFT'S SOFTWARE IS INSTALLED WHEN THEY LEAVE THE SHOP. HOWEVER; THE ERROR WAS ENTIRELY MY OWN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE COMPUTER PARTS TAG ONLY INDICATES THE LOADED SOFTWARE IS CURRENT; BUT DOES NOT ADVISE WHAT ACFT SOFTWARE; B757 OR B767. THE L COMPUTER WAS INSTALLED AND THE ERROR WAS MADE IN CROSS LOADING THE SOFTWARE FROM THE REPLACED COMPUTER INTO THE R EICAS COMPUTER. NOW BOTH WERE LOADED WITH B757-200 SOFTWARE. THE MANUFACTURER SHOULD HAVE HAD A CHIP INSTALLED TO ALERT THE TECHNICIAN AND CREW OF THIS SIT. THE FAULT WAS DISCOVERED THAT NIGHT IN A STATION MAKING AN OVERNIGHT CHK. THE TECHNICIAN MAKING THE EICAS COMPUTER CHK CAME UP WITH HYDRAULIC MOTOR GENERATOR VALVE FAULTS ONLY BECAUSE THE B757 DOES NOT HAVE THIS SYSTEM.