there's no such animal as a vented sending unit, the one you have is what's right for '56 - like this - the "vent" is where the gas line hooks up, the earlier tank drew the gas from the bottom of the tank, so no tube on the sender

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot