It shows the travel (i.e., stops) being the same for the first gen and the 3rd gen performance (i.e., Z28) boxes. The T bar diameter determines the effort. It has to twist (torsionally) to open a valve or maybe it's the other way around, the more it twists, the less a valve is opened. The articles at this link are all rearranged from the last time I studied them so I couldn't find the part on t-bars.
