wrote
My question is how do you measure the angles of the control surfaces to
see if they are within tolerance of their deflection angles?

The easy way is to find someone with, or buy, a "smart level" that
electronicaly reads out the degrees of the surface it is set upon. A real
handy tool to have around, for many other purposes. I would get one that
has a small removable core with the guts, that can be put into different
levels of many different lengths. You can also make a widget using a
protractor and a plumb bob hanging down from it's center pivot point. Make
sure the aircraft has been blocked up level, and stationary.

Check that the wings themselves were rigged correctly, with the same angle
of incidence, if it has removable wings, and that the trim tabs are where
they are all supposed to be.
--
Jim in NC