The high torque GM starter has a housing a little longer than the standard one, and there was a 3/4" long copper tube between the solenoid and the motor connector. Aftermarket replacement solenoids came with that spacer included, which could be used or not, depending on which starter we were repairing. There is also a GM starter with permanent magnets instead of field coils with a much smaller housing diameter. It used a planetary gear reduction section between the armature shaft and the drive pinion. Its only advantage was a considerable weight reduction over the ones with field coils.
Jerry
