I was just wondering if the block pistons crank etc. are different in a Gx compared to a standard 1200 engine

reason is that my Gx block looks to have a bit to much corrosion happening in the water gallaries
So i was wondering if just putting the Gx head on a standard a12 would be a good idea, or if there are any Gx bits worth swapping to the new block

Are you saying that the cast iron block has corrosion issues, but the aluminium cylinder head is OK? That's a new one on me.

The 1200 GX [with a capital X] engine has more compression, but my parts book says that the pistons are the same, so it must be the head that provides it.
The camshaft is diferent & i would not lose it if i were you, even if you don't use it.
The coolant suction pipe at the front of the block is diferent too as it has an extra fitting for the heating system in the inlet manifold.

These seem to be the only things that i can find that are diferent between the short block 1200 & 1200 GX engines. [1970 to '73]
The cylinder head, & just about everything that is attached to it is diferent, but you already knew that

thanks of that, havent had too much of a look at the head yet, but from what i could see it looked ok

do you know if the GX cam fits in the standard block, dont know if ill get a new cam or not yet
and i guess you can just heat up the coolant suction pipe and bronze it onto the new block

Well, since everything else about the block is the same, then the cam will fit without trouble. The diference between the two cams is the valve event [the grind] As for the coolant pipe, just give it a few taps around the outer end with a SOFT hammer. Rawhide is probably best.

This pipe is a press fit in the block & you need to loosen it GENTLY. Once it starts to move, grab it with your hand[s] & gently work it out with small movements & a lot of pulling.
When you reinstall it, you may want to place a few stake marks in it to help hold it & use a suitable sealant. Make sure that you correctly align the extra water fitting otherwise the hose from the manifold will be either kinked, or stretched.
Drive it home firmly with the soft face hammer again to prevent damage to the pipe. When it comes to sealants, I like Cat red myself & that's what i used on mine 20 years ago. It has never moved or leaked since i refitted it.
[Cat red = Catarpillar liquid gasket. It's red in colour & available from all Catarpillar tractor agents.]

Thanks for the advice Dodgeman
I'll see how i go