I have just acquired a IFS SET up, but don't want 5 stud, will mk3,4 5 cortina hubs fit, and are the uprights different to cortina in their offset

depends whether its a sierra P100 or a cortina P100.

Cortina P100 (double wishbone) and Sierra P100 (strut) types, like the cars they were based on are totally different.
I believe the Cortina P100 were based on Granada uprights and the Sierra P100 are struts with Transit hubs.
If you want 4 stud I would go in search of 4 stud hubs.