OK so we now know that you only want info for connection to the sender NOT the gauge. Here is the complete story of senders. You seem to have the correct one for cylinder head mount. After reading the history, Click on "Repair Components" scroll down to "Temperature Sending Unit Lead Repair Kit" to see the connector you need for the pin type. I thought you had the "T" type "Hat" because most internet vendors show that style for 1956. After reading the link here, I see how confusing this 55-56 deal is and that previous owners may change things. Anyhow now you finally have the answer and the place to buy what you need.
http://www.lectriclimited.com/frequently_asked_questions.htm#F02
The 3rd white connector from the top is probably your choice for the sender pin because it can't rotate into something hot because it's round.

P.S. If those studs in your pic are on the temp gauge, they are not for a ring tongue. I do not see threads. You should not take the nut off IMO. You may need what I think I see in the lower right corner of the "Repair Components"/Temp sender unit lead repair kit" picture. I am pretty sure the "L" shaped Gray connector/contact set is for your gauge.
You can also see them in this pic.
http://www.trifive.com/garage/56%20Chevy%20Assembly%20Manual/12-4.gif

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn