Hi Mary,
PP1 or PP6?
First of all, checking the back of the book for sizes ... page 166 ... 2 1/2 inch = Medium; Large is 3 inch. Now go back to the PP6 detail on page 82 where it says 1969- 1971 was Medium size and 1972 - 1977 was Large size. So, at 2 1/2 inch, it might be PP6 1969 to 1971, but for those, a star cut base was used. Your weight does not have a start cut base, so it is not the earlier ones of PP6.
That rules out out any form of PP6, without even considering colour of the ground or the lack of a central "P" cane. So it's a PP1 - and the lack of a "P" cane means it is pre-1978.