The E-locker was the only option.. Not only is the third member/axle housing bolt pattern different, the opening for the third member is different (there's a notched out section to make room for the actuator mechanism)..
It is possible to rework the axle housing to relocate the two bolts that are in a different location and notch out the opening. This would have to be an operation with the axle out from under the vehicle. Here is a link to an article about doing this modification:
http://www.4x4wire.com/toyota/tech/electric_locker/
Another, easier option would be to go with the ARB locker.. Article on installing the ARB:
http://www.4x4wire.com/toyota/tech/arb_locker/
According to the 2000 year 4Runner sales literature, the E-locker was available only in the 4:30 gear ratio.