What will make a clutch pedal really stiff is a high spring rate pressure plate, or an inadequate over center spring on the pedal. Is your overcenter spring from a /6 or a v8 application such as a 340 or such ? Comparing the 6 vs 8 spring there is a huge wire diameter difference, and a huge resulting assist difference as a result.
I think the riveted parts you are talking about is the flat spring steel "keeper" (for lack of a better term) that locates the fork on the pivot. It shouldnt have anything to do with pedal effort as long as everything is located correctly.