I think the only way to find out would be to take better photos and email some of the vintage outboard places in the USA.
It is a really strange one. The lid and tray scream a late 3 hp or a 4 hp, but the clamp and brackets are from an earlier 3.
It may be that there was a variation like on the newer ones. The lids and tray were different if you had a tank attached or a remote one, but I'm blowed if I can find it.
One thing is that the clamp looks ok, if it's just powerhead parts that's needed they should be easy to find.