The thrust angle on a lot of planes is built into the firewall. The fuselage is a bit longer in the front on one side than the other making the firewall have a bit of an angle to the left. When you bolt the engine mount on one of these plane the thrust angle will be preset. Other planes like my original trainer simply stated to add a couple of washers on one side between the motor mount and the firewall to give the same effect. With regards to the OS 61 engine, are you asking if you should mount it on your trainer?? If thats the case, there is no advantage. Trainers with more power usually won't give you that much more speed. It will just climb faster and glide farther at lower throttle settings. Trainers tend to be floaty. With the bigger prop needed for the 61 engine the problem is that the plane will want to keep cruising along in level flight and you may have trouble losing altitude to land. I had that problem with my sons LT25 when I used a OS 32SX engine on the front. Lots of power even in the wind but very hard to get it to come down! [8D]