Hey Nas,

A Z bend at the servo is a good idea but I would go with the retainers for starters. I never had a failure with any of the hardware Hobbico supplied. They make pretty good stuff. Mostly a 90 is easier to get right than a Z if you are new to building.

You indeed must have threads for any clevis. That is how they attach and it is your adjustment point, Bend the 90 or Z as close as you can to suggested then screw the clevis in or out to get the trailing edge (control) surface perfect. Leave enough length at the threads for this without interfereing with a control horn.
You will need to do this again; at least I do; to get it flying perfect with no transmitter trim. Straight and level with no stick or trim input.
Let go off the sticks and the Avistar will return to normal flight if set up this way.
It is a great trainer plane and the manual is very helpful for new ARF builders.
Enjoy yourself with it. It will perform for you.

M