I am starting to wonder if something like the Microsquirt could be used in an ignition only mode. Then you could make maps determined by not just RPM but by engine load, and set yourself up for gathering the parts to convert to fuel injection.
http://www.microsquirt.info/
Not a drop in device and more expensive, but might be worth it to some people.
http://www.diyautotune.com/ to order the Microsquirt.