1970 Chevy C10 Pick Up 292 Fuel Tank Issues

[Bobby Jo]

As stated, I have a 1970 Chevy C10 Pick Up truck. I replaced the fuel gauge thinking that's what my issue was. I was sadly wrong. It has since been suggested to me that it could be the sending unit. I checked the wiring and everything and it looks fine. I saw no bare wires or cracks. I turned to my trusty LMC Catalog to look up the price of the sending unit and saw two different kinds. I have no clue which one I would need. Either a w/2bbl or a w/4bbl...or would just the float sending unit work. Help! I am a first time "mechanic".