RE: 40-50cc engine
Yep.
I removed my DL 50 from my Yak, because the Brillelli 60cc puts out more power, and performs best on that airframe.
There are many 50 cc engines, a few 52, a couple 53, and that's about it.
Then you jump to 60 cc. They put out more power than 40, or 50cc, engines.