Jim, I posted a question a few days ago about wheither a OS1.60 would fly the GP Pitts. I found several people using them, Moki's and a vast majority using gas. I dropped out of the Big gas
burners a couple of years ago. If you want to try gas, a good 50cc will power this with power
to spare. I've run Quadra, Zenoah, Sachs, Brison, US Engines, and 3W. All have their pros and cons. A magneto type engine will run fine, will shake at idle due to timing is set for wide open. They are heavier, and can start a little harder. A electronic ignition has a extra battery to keep
charged. start easy, are more costly, and have more power. They make Pitts style mufflers for most of the popular models, also set up for smoke. The 3 cu. twin 4 strokes are heavy, costly, but sound nice. So suming up, a OS1.60 will fly it, so will the 1.8 or 2.1 Moki. If you go to gas,
either type, you can get a Pitts smoke muffler on most models. Most important compare total weight, with muffler and what ever is needed to run it, power, and cost of each engine. Remember gas is way cheaper than glow fuel, but don't spill it in your car or you will be smelling it for weeks! Hope some of this helps.
Rick