I do think it's very close in 1978, but Borg just edged it over Connors. 1979 wasn't a good year for Connors, as Borg accelerated away as world number 1 and McEnroe was clearly overtaking Connors as the world number 2 before the year was out.
McEnroe voiced his confusion over the Masters timing issue at the time, whether it was the end of the previous year or the start of the new year. Nobody seemed to know. I don't know why they bothered moving the Masters to January and the Australian Open to that dead-end slot around the Christmas period.