As to the tank, it may be brass but I'm not 100% sure. Certainly this one is, but it's earlier than yours : http://metal-polishing-supplies-forum.2302969.n4.nabble.com/Tilley-Lamp-td3928000.html
I called Base Camp in Littlehampton - they were very happy to answer questions and told me that the tank was brass underneath the gold paint, and so should polish up nicely.
So I'll do that then.
Andrew