I still don't understand your problem. From what I see, cdbrown is using a 27" TV (68cm). Your monitor will fit fine in this cab with no problems. If you want an inch and a half on either side, you want a width of 23 1/2 inches. If you are worried that your monitor is TOO SMALL for the cab, all you have to do is change the width of the cab.
Just take the plans, draw them out, etc, and wherever the width of the cab is, change the number to 24 (or at least something smaller than the original size). You cab will now be the width you want. You woudlnt change the height of the machine, or the depth. You'd have to shorten the control panel by the same amount, or just realize it will overhang some more.
Honestly, if you want to change it, thats fine, but I would only take a few inches off and leave some more room between your monitor and side. I only looked at the plans for a second, but it seems the width is 32 11/16". I'd cut it to 25-27" perhaps.
My point is: You really dont need to alter these plans or have someone do it. Wherever you see 32 11/16 (if I am right in saying this is the width, double check) just change it to 28" (or whichever you choose). That's it. done.