Fuel Level Sending Unit

I need a sending unit for my Jimmy, and Its $300 at Auto Zone, but I have a friend that has a Junk Yard, and says that he could let me have one for 20$. I was just wondering if anyone knew what different makes and models would have the same sending unit. Mine is a 97 2wd Jimmy 4.3 Vortec. Would a S-10 and a Blazer have the same sending unit, and if so what years? does anyone know? I was also wondering if anyone knows what this piece is thats also on the Fuel Tank, but its on the opposite side that the Pump and sending unit are on. Its a little black thing that goes into the tank, and its got a little black rubber hose plugged up to it. I was told it was a air hose, but im not sure.

Buy a Chilton's or Haynes repair manual bro.

A unit from the same year and engine will work in a jimmy or a blazer.