the installed performance apparently differed because there was a warning to regard "Error" indications as "meaningless" in the Mk2, but no equivalent warning in the Mk1
If there was a difference in performance we operators didn't experience it.
an a/c at 300' has line of sight up to 51.3NM
While not entirely relevant to the accident, Turnberry VOR would not have been the beacon of choice as it was on the extreme edge of performance, and more importantly, not on the planned route.