Fuel sender question.

[71slowroller]

short version
I have a 71 c10 that came stock with a 350 engine. I'm new to Chevys so this could be a dumb question but I need to know if I need to buy a 4bbl or 2 bbl fuel sending unit so I can get my truck back on the road.

Long Version
I aquired a 71 c10 that has a great drive train but everything else was pretty much garbage (except the body). I replaced all the axle seals, brake lines calipers roters drums pads shoes and installed a booster. I finally got it rolling, insured and put a tag on it and the thing conks out on me about 20 feet from my drive way. This truck has been my buddy every since knowing it could have gave up waaaay beefore I got home.

The issue. Old gas, rusty tank, and sending unit. I've got the tank cleaned lined and ready to go back in, but I can't figure out if I need a 4bbl or 2 bbl sending unit. It came stock with a 350 engine.

Thanks for the help.
Rod