Hi Richard!
I'm hoping to make it to most of the contests this season....I'll see you at Jim Sheffields later this month barring unforseen......
Here is a link to Nelson Hobbies which markets the prospark- there is quite a bit of information at this link:
http://www.nelsonhobby.com/prospark.html
As for mods, you can run the ignition system with the stock carburetor and run glow fuel and then all you would need to do is mount a magnet on the thrust washer and a sensor on the crankcase in front of the carburetor. (BTW this ignition system would work just as well with a 4 stroke running glow fuel.) The spark plug is 1/4-32 threads and just screws right in.
For the gas conversion, I also had to put a pressure tap in the crankcase for the Walbro carb and drill and tap the barrel of the Walbro carb for the mounting screws. I haven't changed anything else on the engine and Duarte (see below) says he's had long term success with the gas conversions with no problems running high oil content relative to most "gassers" at 16:1.
The ProSpark is made by Duarte Cabral and I think his main "target" is military RPV/UAV's but he's a very nice guy and I've spoken with him at length about this system. He recommended that I modify the walbro by putting a piece of brass tubing from the front plate of the carb curved over the top of the carb intake....just a little practice with the silver solder and it was a piece of cake<G>. I ran it on the bench without this mod and couldn't tell any difference, but it was easy enough to do that I did it on my "backup" as well. Duarte has been using this system for over 10 years, so I bow to his experience.
I am pushing him to incorporate an auxiliary channel cut off into the ignition so that you can plug it into an aux channel and remotely shut off the ignition. I have a switch on the fuse side but in case the carb sticks or a mechanical link breaks, I think it would be a nice feature.
I will probably put a "smart-fly" cut off on it in the meantime....just a little more weight to deal with<G>.
G