ORIGINAL: 3DAP

I have a 6 channel that will let you mix say channels 2 and 6. Channel 6 is the slave channel (mixer). Your manual should walk you thru it. Only problem is that it will take away your elevator dual rate capability. When dual rate switch is on high both servos work. when on low only one half works. Or you can use a servo reverser, but like MGLAVIN says linkage geometry has to be exactly equal.
3dap