David, before you go ordering those rather expensive copies of plans, I would advise you to check some of the other sources easily accessible on the Internet, and elsewhere, for such plans.
For instance, I do know that the volumes of the OFFICIAL RECORDS OF THE UNION AND CONFEDERATE NAVIES IN THE WAR OF THE REBELLION do include a very small number of such plans. Digitised versions of these pages are available on the Internet, and you could check these, if you have the time and interest. I do have the actual volumes in my own personal library, and will attempt to do a check at some stage, but with the current season, and some other projects at hand, I may have to put this off for some time.
Additionally, I do know that some of the Naval volumes published in recent years, also include some of these plans. For instance, John M. Coski's excellent volume, CAPITAL NAVY: THE MEN, SHIPS AND OPERATIONS OF THE JAMES RIVER SQUADRON, does include, in appendix 2, a number of ships plans, and I have seen, but cannot recall where, other plans in some other volumes. I am sure that there would be other publications or periodicals which show such plans, as well.