The new tank doesn't have any bung, only the two big in/outlets and of course the overflow bung in the top. See attached picture.
Aha, so the small hose goes to the radiator in the front of the car? - I'll have to follow it and find out if there's a banjo fitting that I can close a you suggest.
Perhaps I can take a picture and attached in a post in few minutes. Working on the car as we speak. :-)