Sorry I didn't answer questions yesterday, Computer problems......
The OS 90 w/pipe, do it and have fun! The YS 120-140? You like little storms of raining balsa bits?? Just kidding..... I think if ya'll want to go with larger two and four strokes the airframe will take it. Just one word of warning: I've not been able to flutter this bird with the Saito 100 at full throttle. You might be able to do so with the larger engines, so use your throttle wisely. There are two mods I'm going to encourage pilots to do, one is personal choice and the other is for fun. The first is to put wood or carbon fiber arrow shafts for push rods and the other is to split the ailerons and make the inboard part a flap. (A-la US 60 & 120) I really liked playing with the crow function and think the BIG BOY could give as much fun too. We are doing some video on Thursday and will try to post on the Morris website this weekend. Will get the pictures on RCU in this thread about the same time.
Terry