rear diff flange

hi ppl im going to be fitting a 200tdi rear prop on disco get rid of the silly rubber donut just looking on ebay and there is two types Earlier Style Square 49mm Height Flange and also a 61mm how do i tell what one i need. im a bit green when it comes to this type of thing. i got a 1994 300 tdi disco if that help.....

the best is to search it by part number STC3723

frc3002 is cheaper only difference that matters is splines not flange shape ,spacer will be needed to as is incorporated in 3 bolt flange