I have this '64 Kent that's identical to my first bass. Sounds great. The problem is that these basses did not have a truss rod. I've tried shims here and shims there and everywhere, but I have been unsuccessful in getting any relief. With no relief, of course, to get the lower half of the neck to not fret out, the action on the upper half of the neck is really high. I don't want to give up, but after 10 or so attempts of shims at different places and different thicknesses, it's getting frustrating. Any ideas or tips?