Hi,
I did a post on this in 2014 which includes routing Here we go!
Might find this useful. The after-market speedo cables are wayyyyyy to long, some as much as 46". I reckon the first (67051-52) was 41.5" from lip of cup to lip of cup, suitable for 52-55 Ks. This enables the smooth factory route running outside the lower frame rail (see page 19 of the early K handbook), up the back of the right down-tube (loosely retained in spring clip, see page 3) and so to the clamp on the terminal plate and on to the speedo.
Next came 67051-52A which I reckon was 42.5" to allow for the raised neck on the '56 up frames to '66 XL, XLH and XLCHs. Then came the 67051-52B which I don't know about!
Anyway, the good news is that Ralph Dollarhite is a speedo repair man and maker of drive cables. He will make you one to whatever length you want that looks NOS. He's ace! Reach him through
[email protected]