well lets keep it simple fixing the servo to reverse itself is a hard fix and you must be very careful or lucky...
the simple fix is put one servo arm on the other side of the servo... wallah it now travels in the same direction
and no doctoring the servo...use a regular y cord to connect the servos to the receiver...doesn't cost much,
takes very little time...and mine flys great...tracks very straight through the air... equal up and down...
when you cut the holes for the servo cut one above the other at a distance to keep the servo arms
at the same throw when they move...imagine a straight line through the model and through the middle
of the servo arms... one arm faces down the other faces up...