The original nuts used by the factory on the GA7 frame number bikes 1960 were a reduced hex plain nut, part 01 6032, which took a 2BA spanner. The top stud on the inlet cover was different from the other 7, with flats machined to allow use of spanner to remove it, giving better clearance when removing/refitting the A10 rocker box.
I dont think there is enough clearance on the cover recesses to fit a full hex nut.