IT is not beyond the realms of possibility to fit a screw-in replacement ball joint. The drag link is hollow. The problems can arise in cutting a thread into the tube. You will need to buy a suitable joint first then determine what thread and size it is. If it is a standard UNF thread, fine. You will then need a taper and second tap. You will then need to cut the old joint off square. Remember that you might still have part of the old joint in the tube. Lastly you need to ensure that the inside diameter of the tube is the correct tapping size.
While you are doing all this it would be cheaper to by a complete unit. Non-genuine ones are readily available.
As to the tappet clearance; adjust cold to 012"
DavidP, South Wales