Does the outer shell of a coil need to be grounded by its bracket the bolts to the engine? I have a pertronix flamethrower which is a little smaller in diameter that the bracket. I wrapped it in tape under the bracket to take up the slack. Bad Idea?
The coil is grounded via the points. It floats above ground even if you have the case strapped to the engine block. Hence, wrapping it does not impact its operation. The thing you might be giving up in not grounding it is radio ignition noise. Take another coil clamp, cut off the sides such that it leaves a "C" shaped segment of it then slide it around the coil. With the "C" shaped shim the coil bracket will hold the coil better and provide a ground strap.