On a bike, it will be tough to hide. I've got an Otis Truckster, with flames. I used an Kohler twin coil, and a double throw relay to redirect the signal from the points. AC Delco M8 spark plugs have 10mm fine thread, so nuts are easy to find. With a twin lung Onan, and dual exhaust, I can get about 18-24 inches of blue flame out inch chrome tailpipes, without injecting fuel downstream, and make it happen all night long. I have never fouled a plug.
Trust me, it looks cooler than it sounds.