The linkage is designed to work as a system. If the longer (lower) arm is what you had with the linkage you're using, then it's what you need to make it work correctly. I don't have a parts book for your year, but I'm willing to bet the 904s had different part number linkages than the 727s. Use the 904 lever, and I bet your problem goes away. As a last resort you could modify your arm (shorten or lengthen) to get the throw you need.
The issue is from mixing and matching parts... it can cause lots of different problems. But you're not the first:
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