The ECU part number depends on the age of the car.
2JZ-GTE engine
89661-30510 = JZS147..Q Oct 91 - Aug 93
89661-30750 = JZS147..Q Aug 93 - Aug 95
89661-30880 = JZS147..Q Jul 94 - Feb 95
89661-3A180 = JZS147..Q Aug 95 on
2JZ-GTE engine
89661-30560 = JZS147..V Oct 91 - Aug 93
89661-30870 = JZS147..V Aug 93 on
The above parts are shown as "COMPUTER, ENGINE CONTROL" on the Electronic Parts Catalogue, so I assume that's the unit you're after. The Aristo also has separate computers for Shift Lock Control, Telephone, Cruise Control, Air Con, Multiplex Manager, Mirror Vibration Control, Tilt Steering, Absorber Control, Cooling Fan, Suspension Control, Skid Control, Traction Control and Power Steering!
A search on the EPCs seems to show that the part numbers listed above are only used on Aristos, nothing else. Would be worth trying wherever you got the engine from.