Thanks for the info, Martin. They look pretty interesting - I can believe the funny looks one might get (that Earl mentioned) seeing the head has no compression adjustment or glow plug (typically).
The fuel mixture - Whew! That's a lot of ether.. It's too bad Ether is so hard to get in quantity. I've been using John Deere ether at a little over $4/can. That would get expensive real quick running those Drones.