"Can anyone post a pic of a sucker rod?"
It is one hundred percent not part of a sucker rod. If I have to I'll dig through the junk yard tomorrow and find a few male and female, but it will be a fools errand. What you found is complex with internal moving parts. Now that you've posted the picture of the small end it changes things a lot, as we don't know whether that is a shaft that snapped off, or a iron surface which slides within the brass to activate the mechanism. It still could possibly be a part of the timing linkage, a contact point, to a large magneto or oscilator off an early cingle cylinder gas engine.