i have an au s2 non irs. i was wandering whether i can bolt a xr diff(lsd/irs car) straight in or whether i need to transfer the gears from housing to housing... any info would be greatly appreciated

They are not able to be changed over without extreme modification.
I'm not sure if the gears are interchangeable. Or the centres for that matter.
All you could do is compare part numbers from Ford spare parts guys. Ask them.