Jim,
I just took a look at the machine again and after I removed the light bulb for the "Fresh Candy" display, I was able to get a tape measure on the top of the glass. I make the actual glass 24 3/4" wide using the good old Stanley tape measure. I also double checked the outside dimension of the glass frame and it is actually 24 and 15/16".
That is about as precise as I can get without removing the frame that holds the glass and getting an actual measurement on the pane of glass. I am happy to do that this weekend if that will help you but I think you would be safe to go with 24 3/4" is a good number. If anything you might cheat up 1/16" but with the frame around the glass you might end up too wide.
Let me know if you would like any pictures or if I can assist in any way. Obviously after you have the 8 pull Display Glass completed, I am an obvious customer--unless you are giving out free samples!
As I said, I can pull the display apart this weekend if you want me to do that. I might actually learn something about my machine in the process!
Tim