I've had a look at this, and can't find any instructions anywhere. However, I have solved it all except for the 6 six-letter answers. It feels like an Araucaria puzzle to me. There are no real words that fit any of them. So I'm guessing they are mixed up in some way.
The way in might be to solve 20d Transport without the groove? (6) or 8d Girl slightly involved with toy boy (6), since all the other six-letter answers reference each other.