Saving Old Seagulls

Hi all, have just acquired a round brass fuel tank.Been siting in a shed for 25 years apparently. It is heavier than the normal round tank. It appears to have not been painted else someone has done a neat job with paint removal. I don't know which model it came off. It is similar to the 1950's round tank.

Question - Did Seagull use a 'solid' brass tanks on any of their models?

Screw on cap or bayonet? Define solid? Photo please.

It has a metal screw on cap and 'solid' is that it is thicker,and heavier than a normal tank. Photo when I can...