The "square end of the pin" has nothing to do with the operation of pin itself or the coupler. Its position should be irrelevant to anything. It is simply a springy retainer clip to keep the round body of the pin from falling out of the coupler and onto the road.
One last question, and then I'll drop out. What is that snarl of fine silvery wire on the rearward end of the lift tab/lever? Is there some kind of trigger under the tab? Never seen anything like that before. Unless you can identify a specific purpose, I would remove it.
Bill
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