What kind of pages are they? this is important because I am wanting to store letters from father to my grandmother when he was in the Air Force. He was about 18 years old and it was during the 1960's. He wrote nearly every 3 days and he talks about President Kennedy and other cool stuff. Are they pages you can slide stuff in, or are they just plain pages? Do they have a plastic film you can peel back and replace? Thank you for your patience with me. M. Wilkerson