i've checked the book for you and the second hand should have a flat bottom
for the date you give and although the pic isnt brilliant it looks to be the
correct one to me. the caseback isnt correct for the year, but it is correct for
the model number 145.022 which was used for many years. its a nice caseback so i
wouldnt worry about it, however, there are a lot of good original speedmasters
out there so if your not sure go for another one.
if your not worried about a specific year you'll get better value by buying
a later one as all the collectors want one made when the space programme was
still in full flow.
hope that helps
Graham