I make the box out of wood and print all the servo mounts. I make changes on the singles by percentage for different servos. Then some are specific the double jumps the stuffing box on a 21 rigger. The multi level is for a tunnel hull.
Better than not buy it. Take all your money and start a prop company. You could make props for people with undersized shafts like you. Then everyone can critique your props when sitting at the keyboard with their coffee .