Fritz is going in the right direction w. his recommendation. Here are some additional thoughts...
As most others, I set my collective and cyclic linkages so that they give me 0 collective/neutral cyclic for mid stick/50% output, while being as close to 'rectangular' (i.e. parallel and perpendicular as required) as possible.
I've been able to reproduce this setup by dividing the linkage assy's into two groups; those above and those below the swashplate. For a moving swashplate setup, I try to center the swashplate in its potential range of travel, or slightly below it, so that I can get a bit more +'ve than negative pitch. Then I adjust the linkages working from the swashplate to the head, and from the swashplate to the servos to give the proper geometry.
Before I worked out this systematic way of setting things out, I found that I had to iterate a lot through the linkages to get the right geometry AND travel AND centering. You may still have to take a couple of passes through the linkages, but you should end up pretty close from the start.
Hope it helps!