Take a look at that guy's Avia, and look closely at the servo installations in the wing. There are a couple of things to notice.

They cast fitted blocks that retain the servos. They fit the servo well and the servos themselves like they were made for them both. They were. TopmodelCZ recommends Hitec 82s for the flaps (metal geared) and ailerons. At first glance those 8 blocks look pretty much the same. They aren't. The pictures show that some are 11mm while the others are 13mm. The pictures showe them used in different places.

Also, the pictures don't show both flap servos. If you wish to use a simple Y harness and not have to use a reversing Y, you'll do what most of us do and install both servos 'facing left' or both servos 'facing right'. If you do that, take a look at the 4 provided servo well/pushrod covers. Items 2-41. You have a decision to make about the flap servo install and 'reshaping' one of the 2-41s.