RE: Few Sig wonder ??
dubro 4OZ will fit nicely either with the firewall backward, just tilt it a bit to clear the wing
if you don't move the firewall backward, watch out to not make the nose too long due to the .25 engine, the short tail moment of the plane could reserve you some surprise during the flair.
the 85BB is ball bearing and a little bit more torque than the 81
of course other servo will fly this plane, but I can only tell you what work for me.