The original table was about 25.5 inches tall which was too short and also the sides of the table were only about 3 inches tall at the smallest point, which is far too shallow for a drawer. The depth and length were perfect at 24 inches wide by 19 inches deep.
With that in mind I drew this plan to modify the table: as you can see, the drawing is of the front of the
table showing the original legs plus the extension and the front panel with the opening for the drawer. The back is identical to the front except for its a solid board and the sides are the same except only 16 inches long instead of 21. The legs needed an extension of 5.5 inches to make the total height 31 inches. The sides I enlarged to 8 inches high to give room for large drawer depth of 4 inches.
I went to Rockler to buy the lumber, as they had various sized pieces of .75” thick poplar on sale that day. I used the table saw to rip the boards to the proper width and the miter saw to cut them to the needed length. So all laid out together it looks something like this:
So assembly time! The first step was to glue the front panel together to make the outer dimensions 8” by 21” and the drawer opening 17.5” by 4.5”. Just glue the ends of the wood that will be touching and clamp the heck out of it to be sure they stay aligned properly. Something like this: