Bob,
The first thing to do is identify which unit you have in your car.
If you have an aftermarket unit, my guess is you'll need to remove it entirely, because what you are doing is replacing it. Again, the Pertronix only needs what is indicated in the instructions. In your case it would be the + wire from your ignition switch, a coil, the distributor, and the ballast resistor. If you switch to the Pertronix coil (higher voltage than any of the Bosch coils) you can eliminated the ballast resistor as well as it is balanced to work with the Pertronix.
There are many people here who have completely original and conventional ignition systems, and have for years. They'll tell you, as I do as well, that you can't overcome problems somewhere else on your car by the addition of a Pertronix. A worn distributor, or a fuel problem, or a voltage problem because of the ignition switch, or any other number of items can contribute to "runnability" issues and the Pertronix will not solve them.
The Bosch system that Jeff pointed out was fitted to 1970-1971 280 SL's. I don't have one so I'm not familiar with it. Note that the late style transistorized ignition is described in the Wiki Tech Manual
http://www.sl113.org/wiki/Electrical/TransistorIgnition You might have to be a full member to access, and it is access to things like this which make the membership fee worth every $. You should consider it...
A lot of the aftermarket units went to breakerless or "no points". They fall into two main categories--optical switching like the Crane unit
http://cranecams.com/index.php?show=browseParts&lvl=5&prt=160 or "hall effect" switching such as the Pertronix. The hall effect uses a magnet ring placed over the distributor shaft, and as the magnet approaches the proximity of the unit inside the distributor, it switches. I had the Crane, worked flawless for 5 years. Then I switched to the Pertronix, and that too, is working fine.
The two units most people here use are the aforementioned: the Crane, and the Pertronix. I know there are others out there, and the latest rage is the 123 distributor.