I think it was Man Utd at home 5th April 1977 which would make sense as my dad worked on Saturdays and that game was on a Tuesday - a lot of my early games were midweek but I started going regularly in 78-79
I know I was definitely at Everton 2 Man Utd 6 on Boxing Day 1977. We started the day in 2nd and Utd were 14th and we were 5 nil down after 70 mins

Just looking at "Everton Results" we played 10 games in April 1977 and finished the season with 3 midweek home games on 16th, 19th and 24th May - we can't even blame Sky !

Crowds were so volatile back in those days
Mon 16th May 20102
Thurs 19th May 36075
Tues 24th May 25208