Here is my choices: (DA-50 would be #1, but since you don't want)

1 - ZDZ50ng, pulls out better than my DA-50 in my 30% yak.

2 - 3w 55 (6hp), 4.2lbs, $535 (I have the 3w60 and it is a stump puller in 18lb plane)

3 - BME 55...but..seems the wait list is almost a year now..extremely light 2.1lbs. (may not be available yet)

4 - G62- by Ralph. I have in my Patty wagstaff...can you spell V-E-R-T-I-C-A-L!! Ralph can save some weight
by using his ignition, starting then a breeze. I turn a 23x10 prop. New G62 available discounted in a few places.

Additional comments: DA-50 is in my book the #1 choice, not only for performance, but weight, company support, and lastly highest resell value.
The ZDZ50ng with new porting pulls harder than DA-50. There are some threads from other owners to support this. RCShowcase provided steller support, both online here as manufactur rep, and website. 3W engines are fined machined German made engines. (I'm not convinced yet about quality of ignition yet). I get good support from both Aircraft International and Cactus Aviation..althought AI is now having an huge anniversary sale..on lots of 3W engines.

There are alot of engines in this category (50-60cc) and what ever you decide, good luck. I'm sure what is to follow is another members view(s) on a whole different set of engines based on their experience/knowledge. If Dick Hanson chimes in, pay attention..he is one of the best!

Bobzilla