I have 138F Johnson Sliding Bypass Door Hardware. I bought two 30 inch solid wood doors, and they are top mount and comes with 4 #12 1-1/4 long screws per door. The door feels like it weighs around 70lbs. Can these 4 screws hold a 70lb door that's top mounted?
As long as it is a solid wood door and not a veneer. Drill the proper sized pilot holes too, so the door rail does not split.
The only thing you may want to be concerned about the screws are is the one on each roller that will go into the end grain of the stile. If it was a longer screw, it would be good insurance. End grain does not hold a screw as well as the grain running perpendicular to the screw. There, a 2 1/2"-3" screw would be well placed. Running it at a slight angle help cross the grain a little too, making it grip better. That trick will not be needed on the other screw.