RE: Engine Recommendation for Yak 73"
The 1.60Dz will shake the wings off your Yak.. You may want to think about soft mounting the engine? I soft mounted my OS 1.60 FX using Dubro soft mounts.
I think you'll find that Quique uses the Central Hobbies NMP muffler on his YS 1.40.
Cheers
Jason.