First you need to get it as close as possible mechanically by adjusting linkage positions on the various arms and horns. THEN, if your radio has this feature, you can use EPA or End Point Adjustment. If the model design calls for differential (more up than down or vice versa) this can also be done at the servo output wheel/horns. I am going to have to leave it to MinnFlyer or one of the graphic guys to draw that up for you. I hope this gets you started. It's easy to do but hard to put in words.
On reflection, what you described really is a differential situation and not endpoint so disregard that part. You need like a 6 arm output wheel and to connect the rods on the arms forward of the drive axle. Could really use a picture right now couldn't you, I could. I'm gonna try to hunt down a picture for you if nobody else posts one.