HiVolt....I hesitate to suggest that anyone attempt to rebuild an overdrive on their own the very first time. Even if you have all day long to mess with it, you can easily get some of the parts installed incorrectly.....or forget a small part. Ask me how I know!
Ford had a halfway decent shop manual in those years that showed how to repair the OD trans. You have to look a little harder to find one that is specific to the T-86 version, although the basic parts are the same for the OD section. Since you will have to tear down the entire trans to get to the cluster gear etc, having the correct pictures for the T-86 would help. You can see the basic parts drawing on our website. Here is the link:
http://www.vanpeltsales.com/FH_web/F...60-272-292.jpg
http://www.vanpeltsales.com/FH_web/F...D_1955to56.jpg
Let us know if you need any help on parts.