hooking up expansion tank?

The Harrison expansion tank you posted a picture of is a Corvette part.
The 2 large nipples connect (in line) to the heater core inlet hose. Of the 2 small ones on top; the one under the filler cap is an overflow, and the other one connects to a similar nipple that is on top of the radiator as the Vette radiator that uses this tank has no filler cap.

Hope this helps.

George