Well now you have opened a can of worms. The 1200GX head was oval port with heart shaped chambers, double valve springs with the bigger valves. Since then the casting has been used on less
sporty models and thats where things get confusing. Most of the later GX heads didn't get the extra valve springs. The chamber volume will have been altered with extra thickness in the head
face and a circular section around the chamber face. This can be machined off to gain the correct shape and comp ratio. Most of the later GXs have 2 water holes below the inlet ports, these
are for heating the inlet manifold. Early heads didn't get these so if you find an early twin carb manifold the holes may not get covered and you'll have to get them welded. I've got GX heads
with the round port chambers as well which came off Japanese import A15s which aren't exactly desirable. There seem to be many different combinations used in different markets around the world
with the US getting heads with extra smog ports as well. The key to getting a good GX is the oval inlet port up nice and high (some oval ports are in the round port position and have big water
jackets around them)and the heart shaped chamber as long as you have these you can build a good head. Are you still confused?? Have fun in OZ and good luck finding some shocks...