I think it's the Dyna III (made by Dynatec) that most use to cure the double image. That is if they are going to use the electronic ignition conversion to cure this problem. There are two magnets for the Hall sensor and they are set separately. I had the hardest time getting this to work and eventually had to use another method after I blew the module up by trying to balance carbs by removing plug wires. (with any electronic system do not balance carbs by removing plug wires) (we are supposed to not ever do that with points/condenser systems either, but for different reasons)
There is another method for curing the double image. It is not exactly fixing the original problem sort of thing but it is closer to fixing the original problem. Here is a page from Duane Ausherman that talks about the whole issue. His article is about the /2s but then he explains the differences for the /5s and the basic idea is what's important anyway. After you read this if you want to discuss it more then we'll start on that.
Like I mentioned, I tried the electronic conversion like you are planning and this is maybe the most common solution for most but I had trouble with making it work and ultimately I was happier I think with being able to keep the points and later adding a Booster box which has some advantages over the Dyna III. (Booster costs about $80, Dyna III cost almost $300) ( just a guess really)
There are several other people here who went with the Duane Ausherman method of fixing the double image. They'll be around shortly.