Yes the xr4 hubs can be swapped direct for the present ones, along of course with the calipers and discs, won't be a awsome improvement though.
Putting on 2wd cossie discs and calipers is easy, as they fit straight onto 2wd hubs after you have tapped out the hole that holds the normal sliding caliper, as the cossie ones are bolted to this lug, think it's either 12 or 14mm, then bolts to suit, the hole conveniently is already the correct size.
This is what I did to my 2.0GL auto, first with xr4i discs then 2wd cossie stuff.
In this answer I am assuming you mean xr4i and not xr4x4, as as has been said xr4x4 stuff is different.
The abs ring is normally present even on cars not fitted as it is part of the spindle/hub, was on the ones I did anyway, but if swapping over stuff mix and match can always be done.
The most effective £ for £ improvement will be to use grooved discs and ebc redstuff ceramic pads.
tabetha