Back then we'd get probably about 5,500 for an 'average' game, maybe 7,000 ish for bigger teams like Aberdeen and Hearts and over 10,000 for OF matches although Rangers nearly always brought a bigger crowd than Celtic.
Just taking a quick look the famous 1-0 win v Celtic in the Scottish Cup when it was blowing a gale and Tommy Coyne scored the winning header had an attendance of 14,061.