i may be wrong, but id assume that you would have to get a rwd fitting kit like whats used in the escort mk1 and 2s which moves the thermostat as it is in the way otherwise?
personally wouldnt bother with ZT for a sierra would go YB as for the money your going to spend building one you can get more out of a YB. its just my opinion though, may be worth asking on the sierra owners club website.