Is it me or are these non-matching? The seller says they are matching 3 screw SU's from a 70 Z. If memory serves, 3 screw carbs came later. The bolt pattern is different it seems and the float bowls are both on the same side. I don't see how the linkage can go between. I'm at work or I'd go check my 70 in the garage... Sombody please tell me I'm dyslexic. thank you in advance...

Some one else has got a set just like them. Only Opposite. They are both aft carbs.

Hard to tell if they are both 3 or 4 screw. And you are correct the 3 screw came later. The reason it appears that the bowls are on the same side is because one is facing up and the other down. Notice the butterfly valve of the one on the left and the one on the right is the piston.

No, they are a pair. The one on the left of the picture is sitting with the manifold side facing the camera, the other is sitting with the airbox side facing the camera.

These carbs are not for a '70, they are for a '72. Note the coolant passage to the nozzle area on the left one.

In general, four screw carbs were used in '70 and '71, three screw carbs in '72.