zenki axles are the same as T-18 (both are early term/skinner) The only exception is the diameter of bearings used, as they vary depending on weather your diff is disc brake(larger bearings) or drum (skinny bearings)......
You have to machine down the area where the bearing sits on the T18 axles in order to get the commerically available, non-Toyota, Zenki bearings to fit. May be a different case with the official Toyota bearings. Dont have to machine it down much, but from memory it was about 0.6mm overall.