The dual elevator issue has been resolved as the RDS8000 does have the ability to work split elevators with separate servos. as well as they can be reversed.... See old dogs ( me ) can still learn something new. After some research I found how to do it.

Regarding the servo twitch , try swapping out the twitchy one with a known good one that does not and see what happens. If the twitchy one is a used servo
; it could be a dirty pot, would be my first guess. I agree that the servo reversing harness is not a good way to go . Seems to have issues with certain brands of radios more than others