ticking that ceases at higher rpms is almost always the lifters. they wear out and the tolerances get slack, so at the "dead level" in the cam (when it's not pushing at all) there is a gap between the cam and the lifter and you get that metallic click. The reason why it goes away at high rpms is because the lifter spring doesn't rebound quickly enough to reach the equilibrium point.
I've never done valve work before, so I may be off a little. I'm replacing the lifters in my 3000GT next weekend, so by then I'll be a pro, but from what I've seen in the 1.8L BP when I broke it down to change the valve cover gasket, it did not appear to have any rocker arms. I think that rocker arms are only used in pushrod engines where the camshafts are below the crankshaft. In the BP, the cam lobes directly contact the lifters, which sit right on top of the valves. I think that is right, but somebody correct me if I'm wrong.