Well they do make a small transister ignition module that you can use with a small ignition coil wound for 4.8v instead of 3v. The overall size is pretty small. So it has a lot of promise.it is a fixed ignition timing unit, but that shouldn't be a problem with the smaller engines though.It uses a magnetic pickup and a hall effect sensor too. The units may be perfect for smaller engines. But I don't know how well it will work with the fixed timing setting though, until I try it.

I actually bought one, but I need to put it together and come up with a way to mount it on a engine to see what happens.
http://www.jerry-howell.com/IgnitionModules.html