The documents for the GRT servos are pretty easy to understand and they emphasize not to over center the servo arm or you could break things. When I set mine up, I aligned the servo arm pivots with the idler arm pivots for both roll and pitch. The tube clamps were installed on the idler arm to match the outermost hole on the servo arm. If this is too sensitive I can always move the rod end on the servo in.
It's really not that difficult, just stare at it a while and you will come up with a plan... thats kinda how it worked for me