3/8 sending unit

http://www.gastanks.com/1963-76-A-Body-3_8/productinfo/SUCR11-38/
http://www.gastanks.com/1963-76-A-Body-3_8/productinfo/SUCR11-38SS/

not sure, those are something i was looking at. i think if it has a 2 lines, the 2nd one is a return line