Hi John
I have a Milemarker fitted to my series 1. The only issue I had when fitting it was that the water pump gasket was not standard and therefore had to fabricate a new base plate for the pump (air con mounting place).
If you have a standard pully, then you need to upgrade to the one with two grooves. Disco ones are not cheap, but the defender one fits. Sorry, can't find paperwork to give you number. If you call the guys at Alfred Murray (milemarker), there'll tell you the part number.
Good luck.
Chris
ps: one point, sometimes when using the winch, the hazards come on. You need to lock the doors with the key, and open them with the fob!!!!!!!!!!!!!!, works for me