A 120 would be too much for this jet.

I have a K80 in mine and it flies great. As far as servos, If you look at the manual, it gives dimensions of servos needed. You would have to research the torque of a given servo dimension to fit it in the jet. With that said, here are the servos I used in mine.
MKS HV69 High Voltage Ultra Torque Digital Servo 141oz @ 8.4v .10/60deg
These where for the elevator, rudder and nose wheel steering. I had to modify the mounts which needed done any way to add some 1/8th inch ply. The rudder I made a mount in the vertical fin and used the servo mount they provided only as a cover as it was to flimsy as a mount.

MKS DS1210 Digital Standard Servo 138oz @ 6v .12/60deg
These where used in the wing on the ailerons and flap. Dropped right in also had to modify the flap mounts with 1/8th inch ply.

I also added 1/8th inch ply to the turbine rails. What they call ply is some thin balsa with some sort of filler in the middle and screws would not tighten without stripping out from what I see.

Joe