Since doing stuff like what you are talking about is how I make my living I will throw in my two cents worth. First doubles are not like bolt guns and require some special tools to do the job right and not damage the gun be it rifle or shotgun. For example you have to have a way to compress the main spring in order to remove the hammer (Tumbler) pins or screws with out damage. It is also best if you have blocks to hold the action when working on it. Browns book on building double rifles on shotgun actions would be very helpful to you and gives patterns for making many of the tools you will need.
I am not saying do not take your gun apart but I am saying get the tools and knowledge first or you will be paying some one like me to try to straighten out your mistakes.