Heard it can be bandit country so might be wise to go with friends, commenwealth games course is going to be there and ive heard the trails are good. You tried contacting one of the local mt biking clubs glasgow etc....?
It's not far away from where I stay (about 6 miles)so maybe I'll pop out and have a look over the weekend.
Here I found picture of that circut it might give you some idea?
Actually I was around Cathkin once a year ago with my neighbour but on road only. Very nice place but so dodgy area below. I remember some drunk neds with golf sticks when we've stopped to rest at the top car park (don't think they were from golf club) As Gazz said better go there with some friends.