mates 90 with duff rear diff

A mate ha a 90 with a duff rear diff, I have a three hole flange diff (early disco I think that looks Ok on teeth and a lot tighter than duff one) Only prob is 90 diff has 4 holes for prop and a four hole double UJ rear prop
Can we just swap the flanges over, if we do are there any spacers etc needed and will I have to set any dimensions when fitting the 4 hole flange.

Also how do you get the centre spigot out of the three hole flange!

Thanks in advance
TH

Assuming 300tdi I just removed the 4 bolt flange and the spacer behind and swopped them over.

To remove the 3 bolt flange I cut round the 3 bolt flange centre pin thing, and spread the area with a chisel to remove the centre thing. Theres a few threads on removing it properly, but mine was stuck fast, as its not needed I saved the hassle and used the above method!