I doubt you will find someone with the exact measurements you need.
My suggestion would be to take the standard frame and scale all dimensions down till the ‘top beam motor distance with sprockets and space to put on the chains’ is maxed out with your longest wall.
I don’t know what the usable cutting area will be, but think it will be more rectangular (landscape) than square.
What is the height (ceiling) usable?
If you’d like to dig deeper here are 2 links I found:
→ Frame Geometry Question
→ Is it true that there is an optimum ratio between width and hight of the frame? - #49 by Gero
Regards, Gero
Edit: Feel free to keep asking. I found this the most helpful Forum ever.
Edit2: I tried as good as it goes with beer but the Friends here will correct me. Scaled my ~ 11.5 top frame to ~6ft and got a ‘sheet’ of ~ 4.2 x 2.1.
Now take of the ‘issue zones like low corners, top middle and a bit of top corners’ and reduce by the amount you need for accuracy depending on what you want to make.
You could be better off with a horizontal machine. Will not name them, because I don’t get money from them, but PM I might.