Go to Radio Shack and buy a piece of RG-8 or RG-11 coaxial cable. Cut a piece about 10" long. Strip the outer covering off. You will find a nice shiny copper braid. Slip it off of the inner core. All you lack at this point is finishing.

Check around and find someone who is into ham radio or CB. They usually have a spare piece of coax that can be used. Even the smaller RG-58 or RG-59 can be used.

Before you solder the braid onto the Bosch cap, you will have to remove the plating on the cap or it will not accept solder.

I assume that you are having ignition noise or you wouldn't be going to all of this trouble. I can't remember whether it was Bill or Terry at CH Ignitions that told me about this trick but it certainly worked. I was having some ignition noise with a G-62 which does not have a shielded spark plug wire and cap. I was told that most of the noise radiation was from the area of the spark plug porcelain and that I needed to shield that area only. I wrapped aluminum foil around the spark plug and secured it with nylon ties. That was about 3 years ago and I never had any more radio noise. I'm sure the plane has over 100 flights since then. This is so simple to try that I would do it first and range check to see if it fixed the problem before I would go to all the other trouble.

Ken