I sold my 4th & last Do for $50. .60 size w/ OS 1.08 & ready to fly. I have used two OS 1.20AX's & they are just a little stronger than the old 1.08. I have a used OS 1.20AX for sale here on RCU, it runs great and has plenty of hours left on it. Asking $170 or B.O. I wouldn't hesitate to put the OS 1.20AX in a .60 size Do, 2 strokes rule for 3-D, you just need to go up a little from the recommended size though, I have flown 2 .60 Do's with OS 90 2 strokes & they flew OK, a little marginal for long hovers though.