i had a saito 150 in the nose of my plane and installed a mld 28. the weight is almost the same. when you weigh the saito, muffler and engine mounts vs the entire mld with ignition everything just about the exact same. im curious on the os 120 i don't have one but how could it spin 9400 rpm with a17/6 when the specs call for 9000 rpm peak with a 15-6 recomended prop.http://osengines.com/engines/osmg0650.html have you tried using 30% heli mix on your saito 125 on that showtime. that mld will destroy that cowl because it is large and will require alot of cutting.