Gary,The back-hang side rails should be lower (2-3") than the elevation at front header to keep the door from closing when not hooked to an opener (springs/torsion bar alone). This is a safety feature installers are taught when installing doors (for use without openers). Four inches sounds excessive, check on-line with the door manufacturers directions. The new bent center arm should work with the opener, just don't reverse it (the bend end).
I have been hanging garage doors for a long time and unless there is a headroom problem, I always install my upper rails level. I don't drop the back end. If the door is installed with the proper springs, the door will stay up just fine.
If you have enough room above your door, adjust one end or the other like Ron said to get your opener rail somewhat level. That being said, I have installed plenty of openers where the rail was not level due to lack of headroom clearance. The opener will not know the difference.