The pic above shows a pair of Model B rear motor mount torque rod brackets. Note the two variations of the steel forging boss height.
The one on the left uses a short lower mounting bolt, and the other uses a long lower bolt. Both of the brackets use the same square recess drive upper bolt/screw.
These two styles of mounting brackets are the only major variations I have found, but I have not yet researched them at the Benson Ford Research Center.