Go to the library or your favorite bookstore and look for "Raising the Hunley" by Brian Hicks. I got a copy a t a good price from http://www.hamiltonbook.comb Here' s the most nearly "offiicial" Hunley page: http://www.hunley.org/
You really can't fix the 54mm to meet the correct shape.
If you go to Yahoo.com, there's a very active Hunley discussion groups in their forums.
If you wind up doing research on this project, you will find some most interesting stuff, such as the $20 gold piece that saved Lt. Dixon at Shiloh and was found in the sunken ship or the Connecticut soldier's identification tag that was recovered from the Hunley as well.