The ladder is 18" wide the tubing is 1.16" in diameter. I do not know who made the ladder, it came off of a van I purchased some other parts from. There are no markings of any kind on it to indicate a manufacturer. I also don't own an Aluminess ladder and they don't list specs on their website for their ladder dimensions. From my pictures and the ones on their website it does appear to be a little wider.
New Van: 2000 Ford E350 SMB RB42
Old Van(sold): 1995 Dodge B3500 SMB RB33
Looks a whole lot like a ladder Derek at CCV made me for mine years ago. In fact, your van looks really close to my old van. Really freaked me out when I first glanced at your pics. I've been looking for that van and thought for a second that I found it but my ladder was left side.
Given that you are in Colorado I bet Derek made that one. I know he made several of them when he made mine.
Currently vanless. Weird.
Real name Eric
Finally found a pic of my first camper,
a 1986 Serro Scotty