I also did the 4x4 conversion to a Merkur XR4ti here in the states and it wasn't that difficult. As mentioned above, some small mods to the trans tunnel and front chasiss legs, everything else is a direct bolt-in... front hubs, crossmember, steering rack, dampers, etc. I rear diff ratio is also different.

I expected this conversion to make my car very heavy but it actually lost a few lbs from when it was and XR4TI and now weighs 2900lbs, that's about 200 less than a 2wd 3dr.

As far as the fun factor I do miss the tail out action and smoking the rears but I really have had enough of that during my Mustang days