RE: synchronizing engines
OK, so if you can find a way to install a magnet on each prop shaft you can use a hall effect device similar to the ones used in ignition systems to measure the RPM of each motor. The RPM for each engine can then be quantized every 2 or 3 hundred milliseconds and the result fed to a comparator. Using a microprocessor the rpm of each engine can then be adjusted via a feedback circuit to each engine servo. Violla, an electronic engine synchronizer. Sounds like a cottage industry project for someone who is more into the technology than making any real money.