OK .. I got Plan B.. next guy can do Plan C.
Plan B #
Plan A fails because it is too difficult to attach any mechanical device to the MM-7, without stopping the thing.
So, I take two rare earth magnets, from the spokes of my bike, and attach them to the wheel of the MM-7, carefully, so they are balanced.
This makes the MM-7 have a heavier flywheel effect, meaning it may take more heat and cold to make it work, but that should be OK with the Sterno can and ice. It will spin.
I then attach the 3 watt electric generator that powers the LED light set on the bike, and fix it, with light-weight erector set parts, very close to the magnets, just as would be on the bike.
Disconnect the light assembly, and just use the power from the generator, to power a 3 watt electric motor.
As long as the Stirling can keep spinning the 3 watt magnets, which will only have very minimum magnetic resistance { no debate, it is obvious from just spinning the bike wheel, only a touch of energy is needed to keep it going }, then the 3 watt electric motor can slowly move the Pinewood Derby car, probably shaped like a tractor.
This meas is time is not a factor, and not cost of fuel, in this case, then the "tractor" moves as long as the Sterno burns and ice pack is cold.
It should get there.
Plan C anybody?
P.S. - The bikelight this is real.
http://reelight.com/
It would be the SL150, and I got an extra set of magnets.
I'm not trying to plug things, but maybe somebody will piece these different bits of Green in a new configuration.