I recently acquired a 2L engine and tranny from a junk 75 spider. I am planning to rebuild it for my 72 GTV. In particular, what is the function of the spring loaded lever arm on the side of the pump.

My 72 GTV Spica does not have this feature. Also, is there any other considerations I should be aware, of for the rebuild, compared to my current 72 engine and tranny. Thanks in advance.
Frank