Is that 23.5 inches outside dimension? that is counting the thickness of the sides?  If so that is only about 22 inches of space that you have inside.
Honestly, I think you may need a bigger cabinet, or a smaller monitor.   23.5 inches is cutting it pretty close.  I just got an NEC XM-2960 which looks like it is very similar to yours.  I measured the width and it looks like the picture tube is dangerously close to 23.5 inches.  
I would love to put the NEC 29" monitor in my Williams High Impact cabinet, which is 25-1/8" inside dimension.  But I decided not to because it is a little too big, plus I am happy with my 27" TV in the cabinet right now.  Even the 27" TV I had to persuade in there, I did not de-case it, but I had to modify the case a bit.   The monitor is very different from the TV.  So I do not know how you would tackle that.  But here are a few suggestions:
First measure  if you have not already to see if the decased monitor would fit inside your cab.  Then de-case and try what this guy did.  He just slapped the monitor onto an MDF panel, then screwed the pcb onto another shelf inside the cabinet.:
http://www.willcoxonline.com/mame/index.htmlOr you could just put a 21" monitor in the current cab.  Save the big monitor for another project.
Or you could build a bigger cabinet from scratch and design it around the dimensions of your NEC monitor.