OK, now that I've had a chance to take a couple of photos... Measure the distance between (any) two identical points on your twin carbies (as shown in first photo) and DIVIDE THAT DIMENSION BY TWO (i.e. HALF). The result is the distance that the rear carby is from its original (central) location. Then, cut the throttle bracket (shown in second picture) in the approximate location shown with arrow, shorten it by the required dimension, weld it back together...