Only two questions today

The automotive scopes all used a capacitive coupled connection, that is a sheet metal clamp that clamps around the coil wire. This is not inductive, it forms a coupling capacitor. So you can experiment with that and build one, easy. It is two curved pieces maybe 1 1/2--2" long, like splitting a piece of tubing. The two curved pieces clamp around the coil wire. This gives you your full secondary pattern of all cylinders

Trigger or sync the scope off the coil NEG if you have points or a switching type ignition. If you have MSD I'm not too sure.

The (coil) primary pattern is extremely useful. It shows up dwell from which you can calculate the figure, as well as showing up worn bushings or bent shaft in the dist or bad points or condenser.

Lookee here LOL:

https://lunardiagnostics.weebly.com/uploads/1/0/4/4/10449663/eti_feb77_scopetheignition_1b__1_.pdf