The 40K is throwing me on this one. A 9x42 tank maxes out properly at .75 cu. ft, but a lot of companies put 1 cu. ft. into them. I do not know of any companies that put 1.25 Cu. ft. into a 9x42 tank. That would basically fill the tank, no freeboard and no gravel. Let me think on this one.
Would it help me to find any other serial number, model number or something? If I took some digital pictures of my installation would that be of any value to you?
The most important part for accurate and efficient programming is the media amount. How much resin is inside the tank. If they say it is a 40K system, then the prgramming guide above should be accurate.
I assume you left the old 3 valve bypass in place. Gate valves... neat. The system has a built in bypass so the 3 valve was not needed.
Measure the circumfrence of the jacket as Mikey said, I can figure it out from there. That looks like a 10" tank, but it is really hard to tell from a picture. I could definetly be wrong.