GTR engine is known as a BPD, as opposed to GTX being BPT
GTR has sodium filled valves, semi forged pistons, oil squirters to the pistons, different head, bigger turbo as different from GTX (and probably a few other things i don't know)
TX3 BPT and GTX BPT are pretty much identical apart from the cam covers - one says Ford, the other says Mazda
Check out the thread in this section regarding engine importers