Weber did make the throttle shafts on these carbs in two versions, clockwise and anticlockwise. its just a matter of finding one

One of the single biggest tips to do when fitting the "DG" type carbs on the std datsun manifold, is to open up the mounting flange with a die grinder. remove the bridge section. I ground my one while the adptor fitted as to match port and make everything nice and smooth [not polished]. it's all about air flow.

I was tempted to fit a 40 DCNF [a twin throat syncronous 40mm carb] on the A12 to see how it goes. Just haven't got arround to it yet.