I would get some more screws and try try a torque wrench if the barrel threads are still in good shape.
I have also taken to bedding the scope mount to the barrel with small dabs of JB weld (keep it away from the screw holes!) I find it pops loose with a little torque on the mount, but makes it rock solid until you really want it off. I have also taken to applying a little to the scope rings to eliminate any shifting there.

I had a local gunsmith drill and tap two holes for some 6 hole mounts on a couple contender barrels. On one of them, he hosed up the alignment and ended up up-sizing both new screws so I know it can be done, but replacing with factory screws would be easier and should work very well with a 6 hole base.