Engines to have synchronized firing, there by minimizing vibration (similar to a two cylinder horizontally opposed 2-stroke engine).

Recoil Starter: Pro: Less weight. Con: No ability to restart in flight.

It appears that two Zanzottera MZ 34's will weigh about 5 lbs less than 2 Hirth F-33's

For FAR 254#: It appears that the Zanzottera MZ 202 is 11 lbs. lighter than the Hirth 2706. Both are rated at 65 hp. and will be de-rated to 50 hp. Reliability may be a question but this weight reduction will be needed to keep the economical version of helicopter under 254 pounds.

For SP/LSA: Consider the Zanzottera MZ 301. It is 3-cylinder but weighs only 15 lbs more and can be run at a lower power setting. Also it is a better width (longer) and less vibration. It will cost more.

For SP/LSA: Consider the Hirth 3701. See its many advantages.