If your shoe is over an inch, it's possible that it was once 1-1/8" and has worn down with time. That said, it's weird you had to force the balance out like you described.
It might be better to go with the larger shoe and see how it works. If you are having trouble, you can always grind it down a little until it's to size.
So I conclude I should order -
Series 390, 25 inch, and since the sash weighs 20.5 lbs stamp 2440.
Do you agree? Thx for your help!
I think that sounds pretty good!