The final 2 nuts attach a fairly thin piece of metal towards the bottom front of binnacle to the steering column holder. This piece of metal (or it may be 2 separate pieces) screw into the bottom of the binnacle with 2 screws. Therefore you have the option to either unscrew 6 nuts, or 4 nuts and 2 screws. I chose the 2 screw option, I think becuase the access to those 2 nuts was more difficult, and I could easily get a good grip on the screws.
I think it also made replacement slightly easier, 4 bolts to get through holes in one go, then align screws, rather than 6 at once.
I reckon it comes down to which you can get best access with the tools available to you.
Rich