A lot of race cars use zetecs, and one or two make adapters to mate the zetec to a c-4, i'm sure if you could do that you could do a t-5 just as easily. It'd require the engine to be turned sideways, but that's no big deal. The tunnel is already there, you'd have to fab engine mounts and then buy the spindle kit and rear half kit from kugel and a trans, driveshaft, rear axle, and supporting hardware. Considered doing a rwd c4 zetec in project fastiva, but now I'm thinkin the 2.3 pinto motor could go a lot farther.
A rwd conversion will change every bit of the way your car handles. So to think you can just make it rwd and keep the focus characteristics is a bit farfetched. The sways that come with the kits now are far less than adequate for cornering, and to get a solid rear axle to handle right is a lot tougher than it would seem. Pretty easy to make it act right at the strip, but in the twisties our rwd needs a LOT of work