Saving Old Seagulls

I've been having a closer look at the carburetors; an Amal 416-1 from the Osprey, and an Amal 420-4 from the Kingfisher, with 95 and 115 jet sizes respectively. Given that the 420 came from a motor with a fuel pump, can it be gravity fed only, or is a pump necessary? Are these mixture screws? And if so, why are they only on the 420? They aren't listed in the 416 exploded view, either. Whats going on?

The 420 can be gravity fed provided you don't have a requirement for high fuel flow.

The 1 suffix carbs had both screws not used.
The 4 suffix denotes fitted with the tickover adjuster screw (also requires a stop button), & mixture screw.