TOPIC: Tach for '66 Evinrude 40hp Lark

I want to add a tach to the dash, I found one that matches the existing speedo. I'm asking advice on compatibility with the 2 cylinder magneto breaker ignition engine that has a generator rather than a rectifier. There are connections for Gnd, Ign, and Send. Gnd and Ign are obvious, the Send I assume, is for the tach wire connected to the safety cut-out switch which is wired to one of the points. Correct? There is a dial with settings marked A, B, C. Which of these should it be set to? Would that be for 2, 4, 6 cylinder engines? And is this the type of tach for this type of electrical system? See pic. Thanks!