dvsdev
+1y
Looks like a condenser to me, normally they are situated on the side of the dizzy itself.
If it is the condenser it works like a capacitor in a car stereo, holds a bit of a charge for when it's needed.
Normally you would replace them whenever you do the points and plugs, also just so you know coils are oil filled and don't usually like being heated up which is why it's unusual to see one mounted to the block like yours.
I'd check that too, just to make sure it's not just a dead coil.