My father worked for Mars for nearly thirty years so I know that Mars made Glees. They were definitely around in the seventies and eighties.
Glees were small chewy fruity sweets, highly coloured with a crispy sugar coating shell. They were sold in purple packets. I think they stopped making them in the mid-eighties but I can't be sure on that.
Mars did pilot a 'Mars cake' but it bombed. The sales weren't that promising so they stopped making them but I can't remember the name of them.