The wing joiner can be made "close enough" without plans. Measure the slot in the root rib to get the thickness and height.
Slide a ruler, stick, screwriver, etc into the slot to find out how far it goes into the wing. Measure both in case they are different and double the shorter measurement to get the length.
Guess at the dihedral angle, maybe 3 degrees, and draw the joiner on a sheet of cheap lite ply or even basswood.
Cut it out, see how it fits. Sand, adjust, maybe even remake it until you get a shape that works.
When you're happy, trace it onto good aircraft plywood and make the real part.

OR, got straight to the good wood and 'make it work.'

The aileron servo tray is just a 1/8 ply rectangle with a rectangular hole for the servo to fit in. Trace around the bottom of a servo case and add about 1/8 to the length and width for 'wiggle room' and cut the opening. Make the overall size about a half inch wider and an inch longer than the hole you made for the servo. You can make it even bigger and sand off what you do not need.

I would not even try to make a servo tray for the fuselage. You can run two 3/8 basswood sticks across the fuselage to mount the servos. Many of the SIG kits use this method. It is fairly easy and it works.