Picked up the '64 220s

There is a hook at the end of a small cable that goes on the gear rod under the dash. Make sure that it is attached. Then there is a knurled nut on the gear indicator where the cable enters that you turn to calibrate the indicator positions.

Someone retrofitted those Zeniths on your original car or the entire engine has been replaced at some time. That year and model should have Solexes on a 180.941 engine. The Zeniths were first installed in the 230 fintail on June 1966 around the same time they introduced the w108 which always had Zeniths on the S engine.

My understanding from reading all I could about these cars is that the Solexes are simpler to rebuild and easier to adjust. I rebuilt my Solexes and it was pretty straightforward. It is, however, reported that a well-sorted Zenith is a great carb and if you look at the specifications, the Zeniths do yield 15 more horsepower (on the 180.945 engine).

If you decide to go with the Solexes, you will also need to swap the intake manifold and air hood over. There may also be issues with the linkage and manual vs. automatic choke, although you should have everything you need on the parts car.