yes there is a difference in gas & diesel based on the bellhousing bolt pattern and the torque converter bolt pattern. I'm not sure if it carried across to the 4r100 from the e4OD but there was a difference in the case design for the diesel & lightning e4OD and the standard gasser e4od
Well after some research the id code with 1c3p-fb is the one with out the mechanical diode and the id 1c3p-fa has the mechanical diode.build date on my transmission is BD 1L16 = 2001,december,16