There isn't much room. They mount so the shaft is INBOARD and FORWARD, then install the servo arm using a long ball driver, servo at center. I had to thread the servo lead and extension first, bring it back out the root rib, then pull it as the servo gets installed. It worked best holding the stab vertical, root rib up. Wasn't the easiest part of the plane, but worth it.

Also had to elongate the slots for the servo arms to permit enough travel.