I'm not sure where I got the braid, but it was tinned-copper and used for shielding of electrical cables. It was nice as it can expand and contract quite a bit, so it can just slide over the spark-plug boot, and then be stretched out to be smaller where it covers the ignition wire.

In retrospect, I could have soldered the ground wire to the braid under the flywheel cover and grounded it to one of the ignition coil bolts.

In lieu of soldering (especially if you wind up with stainless steel braid), you can put a slit up the braid for a few inches and twist it into a pigtail, then crimp a lug to it and ground under one of the ignition coil bolts.

One thing more I should do is wrap the exposed braid with a bit of tape or something as it may rub along the roll-bar, and I don't want the rollbar to chafe through.

For anyone wanting to do a quick test, just wrap the exposed ignition wire with aluminum foil. Keep wrapping all the way past the spark-plug boot and crumple it around the sparkplug base. Won't last, doesn't look good, but it will give you an idea if the final version is worth doing for you.