If you have any emails from him about this topic I'd definately keep them.

There is nothing shameful about the naked human body. It amazes me the people that are offended about women breast feeding (even discreetly) in public places.

Having said that, I have never ever seen my father nude. Nor have my children ever come across their father or myself nude. I think if my parents would have used their own bodies for my sex education it would have made me sick. Literally ill.

It doesn't sound like he's planning on being very hands on with the child, and from what you've said, that is a very good thing. I am so glad that you found out about this now rather than when the poor kid was 6.