A strobe is ONLY at best these days a get you a lot nearer to starting mark, I don't even bother to start with, just by ear, but be aware the fastest idle speed is likely to be too far advanced once under way and under load.
Can you adjust the weights/stops inside the dizzy ?
The best method is trial and error, I've been modding advance/retard curves on mechanical dizzies for over 25 years using trial and error to great effect, so in a nutshell just use as much advance you can get away with without pinging.
tabetha