Just a quick question relating to Engine pylons on the Boeing 707.
Whilst leafing through a book of 707 photos I noticed that in many cases the number one engine (left hand outboard) has a different type of pylon.
For example
Strangely, this does not seem to be repeated on the other side
See here
Is there a reason for this? For instance different equipment in the number one pylon - or is it simply a case of interchangeable types?
I would be grateful of any explanations a 707 expert could offer to satisfy my curiosity!