I've got a Remington 721 that I'm thinking about turning into a project gun. My question is about parts interchangeability between the 721's and the 700. I'm mostly curious about the magazine box and the bolt shroud. Will a magazine box from the 700 work on a 721? Will the bolt shroud on a 700 work for a 721? I'd like to put a Winchester style 3 position safety on it. Thanks for the help.