Im missing the part of the linkage which the centre bar comes up and hits to open the throttle on one of the carbs. I was wondering if any other linkages would fit this like from 240z, L series twin su's etc. or what else could I do for this linkage?

Sorry I can't help with your query.
But, is that manifold of an A12GX?
I've never seen one up close. Could you be a sport, and post a pic of the manifold ports with a ruler beside them? I have what I belive to be a GX head. It has taller ports than a normal oval port head. In your pic those ports do look a bit taller.

Bart,
I got a manifold like this which is about to go on my engine. I will bring it round so you can see one in its alloy flesh...