I've taken a closer look at this table, the lower shelf is an add-on, the lighter colored wood holding the machine was made just to hold the machine and fastened to the underside of the table with door hinges. It appears there was a cable lift system on the table at some point, and it's been refinished. It does not appear that the opening in the top was enlarged, if it was whoever did it was somewhat of a craftsman.
Janey, are you thinking this was a Singer table to begin with?