How do I tell what diff I have

[vx Devil]

If it’s the OEM diff still in it,
It should indicate the type on the compliance plate under the bonnet.

Not sure about the 2 letters you mentioned

Will have a look tomorrow and I will post a photo of the diff it is out of the car atm

 

[losh1971]

It will have a 78 in the number if its an M78..

 

[Immortality]

Crown wheel and pinion will 0575 and a serial number on it.