JIM, it's more than forty year.
Going back as far as the 1945 General Election, without Scots seats, the winning party would have been different only in 1964 and Feb 1974.
"In 1964, the Conservatives would have been the largest party but would not have had a majority. Including Scotland, Labour won a House of Commons majority.
In February 1974, the Conservatives would have been the largest party but would not have had a majority. Including Scotland, Labour was the largest party but did not have a majority."
https://commonslibrary.parliament.uk/general-elections-without-scotland-part-1-1945-2010/