Just as an addendum to this, all cars delivered in Canada before MY 1978 had MPH speedos. I'm sure you wouldn't have had a problem, even if they had checked (unless they were trying to be *****s, like above :P).
My car's a 1987 with an imperial speedo and it passed in BC with no problems. Looking around at the locally owned Porsches it seems most have been brought up from the US, with their speedos intact.
Having said that, I'd rather a metric speedo.
