I'm not sure how the JR DS285 servos compare to the HS 65s I used, but I installed my servos with the mounting tabs inside the frame. This allowed a perfectly perpendicular link from all three servos to the swash. I think the suggestion to do this comes from "Finless". You have to install these with the upper frame halves apart and you have to grind down the stem of the ball link attached to the rearmost servo arm (easy to do- just stick a toothpick through the ball and file or grind the stem). This will make the length of the servo links different than what's given in the manual.
You may not want to do this if you've already put the top and bottom frames together and it's not critical, just a suggestion.
Whether you mount them inside or outside, don't forget to set your lowest servo arm on the correct side to prevent "hooking" the main gear. If your throws are set correctly, it won't be an issue, but as a precaution...