Just to clear up on a few things the guys have said above....The motor in the LASER GTX and the FAMILIA GTX are EXACTLY the same. The motor in the LASER TX3 (aus spec) is aslo the same except there are a few differences in the wiring loom and the ECU was detuned.
GTR motor...well, there's alot of myths out there...like the head being different. lol The head shape iteslf is exactly the same, it just has different exhaust valves.
Here is a topic I have put together...I've spent a bit of time on this, and it will continue to grow. Please let me know what you think. Everything on this page is FACT. If it's not mentioned on there (eg web stregthend block) it's NOT true.
http://mazda4club.forumsplace.com/message-20.html