Thanks everyone.Guest, I'm sure you're right when you say "best advice for you, Marion, is to go back to the source and listen to how they pronounced it", except that it's Saturday and I need to be able to sing these on Tuesday, and don't have any people or records to consult. And I'm not above faking it a little.
Mousethief, for what it's worth, the book I found translated the song as "When I Marry Do", not "When I Marry You."
I didn't know you were Amish, Ebbie. Are you still? I spent a year volunteering with Mennonite Central Committee (I'm Anglican myself) so I feel a little connected to you anabaptist type people.
Marion