RE: EF Chin Yak engine/servo setup help
The 821 servos will work well.
Dead sticks are not very kind to the Chinn Yak.
If that 51 is a tried and true great runner and is very reliable in the mid-range (unlikely) then use it.
The OS55AX with a 13x4 or Webra50 with a 12x4 are much preferred for 3D.