Thank you so much for your help.
You've already shed a lot of light on things for me.
The kabuto has some age-related damage, and it has a bullet hole in the mae-zashi that most likely came from an arquebus; it wasn't an arrow.
It looks very, very old from the rust, and the inside is also in bad shape. I don't think this helmet is a fake; I have similar ones from Edo that look worn differently.
So, thank you again for your help.