The carb to carb spacing of the aftermarket manifolds is different from the GX one which means the factory linkage won't fit or work. So unless you plan on sourcing a GX engine, you might as well get the aftermarket manifold & use the SU's that it was intended to use, as an aftermarket throttle linkage should be available for that.

The bolt pattern will be wrong, gx and other oval ports had 4 studs across top of manifold, yours will only have 2. I would get the Gx head first.

Would a problem arise if i just used the gx's manifold with the big oval ports on my standard 1200

There is no GX manifold to fit the standard 1200 engine. Standard 1200 engine has round ports, but all GX manifolds have large oval ports.

But you can buy an aftermarket round-port manifold that fits the GX carbs or SU carbs. Pierce Manifolds has them. Also Mangoletsi Manifolds. And SWM iirc had them in their old catalog.

The most common manifold is the Lynx D1000.

Edward you will need to get the manifold too. You will need to make sure the mainfold you get is the same port stype (round or oval) as your head.

cheers

Hi Fellow Motorists
I would just like to find out can you install the 1200 gx su carbs onto a standard 1200 engine

Thanks Edward