Are 2a and 3 engines different

A quick question, after finding out what engine I have in my new landie so I can change the water pump (long time since I have had 2 1/4 diesel) is there a difference between a series111 3 bearing diesel and a series 11a 3 bearing diesel as checking the engine number it comes up as a series 11a although the vehicle is a series 111.
According to the previous owner the person they bought it of had rebuilt it a few years back.
Once the water pump is done I've got to sort out the terrible heater plug circuit deep joy!!!!!!!!

major parts are all the same

very little, if any differences, especially if they are both 3 bearing engines

not sure but if its an ex militery engine the water pump may be different.

graham
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98 d1 300tdi auto.

Cheers guy's according to the engine number it is a civilian block so should be a standard pump, I ordered one last night.