Regarding the precise alignment of the screw heads:
My Engineers have never installed gauges before and didn't have the proper screws, so they threaded and machined their own.
Production gauges will use standard industry screws instead of the custom made and heat-treated ones that are there now.
Many gauges are installed using only two or three of the four mounting holes. I can't convince the Engineers to even consider that.
Note that certain aeroplanes have their gauges installed with the frames on top of the panel and some are installed from the reverse side and the frames are hidden behind the panel in which case the frame would not be visible at all.
Regarding C Programming:
It isn't really all that hard but knowing the C language will help you much less with gauges that you might expect.
I have run into a few bugs by doing things which should logically work with C but do not because the gauge macros often have not so obvious side effects.
The documentation isn't quite as thorough as one might want. It is pretty much written for folks who already know what they are doing and I am not one of those people.