You do need the tach adapter with the MSD ignition but I found mine was no longer accurate. I purchased Jon Hass's tach adapter but I have not tried it yet, he can explain why the tach adapter is required.
https://www.pantera-electronic...lectriccomponent.htm
Also have a look at his engine controller, it has some nice features, battery charger, ac compressor cut out, etc, plus a tach adapter built in.