[Lynn Eades]

It will be interesting to hear what Michael R has to say.
It could be that your cable comes from a later carrier and was slightly re routed (factory re design) requiring a longer cable.
Btw. the British speedo is different from the Canadian and this might account for the difference. I cannot remember if the fittings are the same.

The 1/4 inch thick rubber gasket behind the dash panel was introduced to help reduce speedo cable failure and also to help reduce the risk of wiring shorts.
I read this somewhere. No recall on where.