the thing about VESA is that, yes... it's standard spacing and size...but it's not standard WHERE on the monitor it is. it may be centered on the panel... it may be higher or lower. assuming it's centered...
get yourself a piece of 1/4 inch hardboard or MDF cut to the size of the original monitor... or a little bigger
drill 4 large holes in the corners so you can mount it to the original CRT monitor's mounting spots.
draw an x connecting the 4 holes to mark out your center.
use a template to mark out where your VESA holes are and their proper spacing.
place this template on your X so that a line goes through every hole in your template... this will get your monitor as close to center as possible.
mark the holes and drill them... use some screws to hold your monitor on to the board.
if you need your monitor closer to the glass, make some spacers out of more wood to have the monitor stand out from the board more.