Thought I would add my 2 cents here as well.
You can find the base plate dimensions for just the ArcDroid here : Base plate dimensions
For the X2 it is 39 4/16" (length) by 10" (width) by 12.5"(as measured from top of rail to the bottom of the brackets) but the brackets are adjustable only to 38.5 each side roughly as they are not mirror images but the same bracket with the same bend on the same side.
