You can do it but you need to do something with the harness and get a new gasket and studs, and such, search the tech section for e-locker retrofit.
Inchworm makes a nice harness, ORS made one as well.
You will need to relocate 2 studs, so drilling/tapping and welding will need to be done. otherwise it bolts right in.

89 4Runner
3" BL, M/T locks, 33"bfg mt, bilstein, Kayline, tubebumper, toyotafiberglass panels
TBI: Elocker,3.4 w/ORS,b+b,S2Sstg2cams,arias pistons,P+P intake,TRDs/c,URDpullies+7th,downey headers,MAPECU2,WEGO WB, SupraMAF,walboro255,stg4clutch, EPaOo2 sim