Lotus Cortina MkII Half Shafts

[Porousblock]

I am building up,an axle for my MkII. I have found 6 half shafts in my workshop but there are 3 different lengths. I know that the MkI half shaft is shorter than the MkII so I can rule out one pair. However the other two sets are very similar but one set is slightly shorter than the other. According to the Ford Parts List there are two half shafts listed for the MkII; a blue spot (for GT and Lotus) and a black spot. I cannot find any 'spot' on my half shafts so I am not sure quite what I have!! (Problem of too much stuff and getting old.............!) Quaife list two 708mm half shafts one with 16 teeth and one with 22.
So, what is the difference between the black spot and blue spot shafts? And where is the 708mm measured from? Any help appreciated!! Cliff.