Best spot to install leveling valve?

As long as the valve mounts horizontal, the leveling rod on the valve is also horizontal and the linkage rod that connects to the suspension is as perfect to vertical as possible, it really doesn't matter. No one oem or suspension manufacturer has ever been consistent and the locations change all the time. The reason for so many different locations is that there is just that many design engineers out there that feel their way is the best.

 

I agree with this, it is not ultra critical. Just to add a little to this, most air suspensions have a pivot point (usually the spring bushing). The farther back you get from the pivot the more travel there is. Most leveling valves have the longer lever becasue they're mount behind the axle. Ones mounted in front of the axle, like off a bracket from the brake chamber or the front of a U-bolt, usually have the shorter lever to match the shorter travel at that point. Many replacement valves have a lever with at least 2 holes and a stamped line indicating where to cut the arm if the shorter one is needed.

 

Here is mine