More than one CB77 tank?

[jehu]

Hi everyone. First post. I have a '67 CB77 and what I believe is a spare fuel tank that is the same as the one on the bike except it is about 1/2" narrower. The tank panels interchange and the spare tank has the same mounting. Was there more than 1 size tank for the CB77? Could the spare be for a CB72?
Thanks.