[WFBowen]

Donal:
The later Solex carbs will have a so-called "split" throttle shaft, as opposed to a single, one-piece shaft on the earlier versions. Look for an adjustment mechanism on the throttle shaft in the middle of the carb body, between the stacks near the mounting flanges.
As far as the float needle, it's probably just a later retro-fit. Remove the old assembly, place it side by side with the new one and see if they're the same overall size. Double check the thread size on the new one.
Bill.