Hi,
well, there is no standard about servo sizes. But I wouldn't worry too much even if the links are not 90°, you will hardly notice it in flight.
If everything's set up as straight as possible, and the swash plate is level with as little electronic trim as possible, recommended angles are set, you are good to go.
Do the trim flight to adjust for the last bit, in flight. It won't get much more precise, the helicopter does not care for exact angles on the ground, there are so many dynamic effects.
I am pretty sure you will be happy
in fact I think we mess too much with perfect angles on the ground, I myself prefer a more down-to-earth setup with only a little measuring and a good part of eyeballing
I mean, a good symmetric setup is the basis, no doubt about that, but e.g. the slight offset from 90° on the links does not do much bad, does hardly change the angles on the swash plate/blades, and it might even help compensating a little for the effect of the servo arm moving in a circle and the link supposed to move up and down straight.
Cheers
Eddi
Born to fly ...
forced to work.