I originally, mistakenly, said that way too much had to be undone to get into the box.  All that has to be undone to get to the business section of the circuit board is the metal crimp tabs that hold the top cover on.  The screws and snap clips hold the board onto the base plate, and these do not have to be removed to gain access to the top of the board (and the PROM).  

If you're going in, be sensitive to the need to suppress static charge: