I have a 2x2 array (24") and a 3x3 array (24").
Your issue is 40". You will not (easily, or cheaply) find a multi-arm mount for this size.
Despite the Octo name, good luck getting a large array for 40".
My 3x3 array is a 3x2 array with a custom bracket to add the top row.
First time alignment is a major pain.
Again, at 40" you're looking for a Civil Engineer's input.