I picked up an adjustable rocker shaft assembly for a big log/big valve head I'm building. It has the tight friction fit no lock nut adjusting screws in it. I noticed while I was cleaning things up that some screws had a much tighter fit than others. So tight in fact that I was concerned the torque needed to turn them might do damage to the assembly. The looser ones make me wonder if they will stay put over time as the engine runs. I also noticed that switching screws from one rocker arm to another can result in very loose fits or even tighter ones. While not a showstopper, I'm not happy with this situation. Is it normal to have a more or less custom fit for each of these screws? I see a different two or three digit number stamped at the screw end of each arm, what is that for? I have also seen lots of pictures of these adjustable rocker arms with a locknut on a different headed adjuster screw. That seems like a better arrangement. They look very much like the Ford FE adjusters. I have not seen any I6 friction fit replacement adjuster screws advertised for sale, but have seen lots of the FE screws around. Are the two screw types interchangeable? Maybe with a re-tap of the threads to loosen them up a bit? Please advise.