I'm revisiting some of nterviews with MK from the STP days. I forgot that Mark wanted to record a blues album with Van Morrison. It's a shame it never happened.
Ed told that story here.
I don't remember 
Van wanted MK to share the credits of "The last laugh", and that petition ended any chance of doing a record with Van Morrison in the future.
Or that's what I understood.
Yes, I remember now. But it probably wasn't Van, but someone from his management.
No, it probably was Van.
I don't fully remember the story but, from memory, and logic, I'd say that it would had been Van's manager talking to MK's manager, but managers doesn't do these things on their own, but because their managed artists asked them to do them.