Ron
I regret I don't know a torque figure but these ball joints are ones you don't want coming loose.
I recently have dismantled all the front suspension and upon examination found the holes for the ball joints were ever so slightly oval. I had a chat with Ray Christopher about it and said he had a similar problem recently too.
He felt the problem was caused by loose ball joints. I do mine up good and tight, however Ray felt that if your uprights are powder coated, or similar, then the tightening up of the nut causes the coating inside the taper to break up and move a fraction. Of course it feels good and tight and you can get good torque on it. But when in use that fraction of broken up powder coating or whatever moves again under load and hence the ball joint is no longer properly located or tight. The hole goes slightly oval.
His soluition is to file off any coating prior to fitting and to ensure you get a good fit.
I have no idea how true this is but the powder coating on my old uprights was breaking up inside the taper.
I am making some new tapers for my new uprights anyway but thought this might be of interest to you.
Malcolm