I am not at all familiar with the 8 track cassettes, only had the 4 track. And for those who wonder what this means, is that you need 2 tracks for stereo, 1 track for the left speaker and 1 track for the right speaker. Then, when at the end, you flip it over and play the other 2 tracks. The 8 track cassette I assume you have a switch to play 2 set of songs on each side.
I always used the 60 minute cassettes, never the 90 or 120. Too much "band salad" we called it. The tape material was so thin to get 50% or 100% more length in them that they did not hold up too well. Maybe expensive players were better.
If you bought a cassette with music on, I think the only size I have come across was 45 minute.
Bill