On lean burn... Megasquirt designs EFI systems for retro-fit. You buy the plans and main components and assemble the brain box yourself.

With EFI and a wideband O2 sensor its not hard to set up leanburn... simply map lean AF ratios and extra ignition advance at light load. Honda I believe sold a car set up this way in Australia. Mileage was great but its not compatible with a 3 way catalyst so it couldn't make US emissions.

The trick is to map correctly so you get the lean burn benefits without trashing the engine through detonation or excessive temperatures. Without a lot of instrumentation and testing this is hard. I've got a little bit of leanburn dialed into my EFI BB. At a steady light throttle cruise its running around 16:1. As soon as the throttle is opened and manifold pressure increases, it adds fuel and goes back to normal operation. I just don't want to push it too far.