I just installed a new tach, and my instructions showed an option for an "inductive pickup" instead of using typical coil connection like I used .
The inductive pickup looked like it just clamped over a spark plug wire like a timing light connection.
I just did a google search for "tachometer inductive pickup" and most of the auto parts chains have them for a little over 20 bucks. Not sure if they would be "brand specific" for different tach manufacturers, but I would assume a signal is a signal and
other than the plug in for the tach, you may still be able to splice to "signal wire" going to tach.......but pure conjecture and guessing on my part. Something to explore