I've been using a Pertronix 12v kit in a 261 for 7 years and a 6v kit in a 235 for two years (about $75 each). There have been no problems and the engines start right up.
I wish they sold (or provided) the protective diode (for surges) that they recommend. It is not available in less than 100 units.
The installation of this kit is very easy (two parts) - Wrenchbender's kit is easier (one part, it looks like) but, as he said, not available for 216/235/261.
As stated by Bill, people have posted that they have burned out Pertronix units and they recommend carrying a set of points/condensor. I've always carried a spare set of points and condensor (and distributor tool) whether I used points or the Pertronix units.
Tim
