All -
Note in the close up that the raw end of the lanyard is visible to the right of and about midway down the breech sight "shaft". No handle doesn't mean they didn't use a peg or stick and simply wrap the lanyard around it for use. Do recall that the first and preferred method of ignition for naval guns aboard ship was the quill primer, which was fired by the fall of a cam driven hammer on the lock. Spring operated locks had been largely abandoned during the period of this war due to a number of issues. Quill primers looked roughly like a golf tee and were percussion/concussion fired versus the metallic friction primers normally used on field guns. Some metallic "quill-type" primers were used but only in situations where the overhead was open vs. between ships decks or in the confines of flank defense batteries of a fortress.
As far as any recess or step for the breech sight is concerned it is my observation that on the big guns like the Brooke there is a "left-right" hole through a block or protrusion that secured the sight to the tube on the ogive of the cascabel. Other examples such as the gun tubes off of the CSS Alabama at the Museum of Mobile and in the CSS Hunley/Lasch Center have "trunnion" sights. These sights are offset and the "front" sight is usually set/screwed into a hole near the base of a trunnion.
The sight bars are as rare as hens teeth. I called every US navy museum/Archive I could identify when I first learned that there was such a thing and finally Carl recalled seeing one (or more) at the Cairo Museum in Vicksburg. The Vicksburg bars are apparently the only remaining examples that are on display anywhere in the US for ACW period naval guns. FWIW, I have a true copy of a three page explanation that was written before the war (J. A. Dahlgren was the author as I recall) explaining how they worked - likely from some of his notes prior to an official printing of some sort. The sketches help a lot. From what I can tell they (at least some) were made as a brass bar on a wooden base.
As for steam, the other great power supply was water driven. An amazing amount of work was done in factories using overhead shaft systems that spanned not only entire floors of those buildings but multiple levels of floors. The torque generated must have been enormous.
FWIW, on a thread that goes back to the initial forum that brought many of us together 5-7 years ago I will attempt to re-state my opinion regarding the spelling of "Fuze" vs. "Fuse". At the time I referred to multiple period-original sources (encyclopedias, military dictionaries, gazettes, ordnance manuals, etc.) in my conclusion that the proper period spelling was/is "FuZe" versus the commonly encountered "Fuse". I don't care what Microsoft, AOL, etc. spell checking thinks, in fact the proper spelling is with a "Z". After all of the fuss and flying feathers, expressions of opinion and any modern sources have been examined I would invite the attention of anyone who actually gives a hoot to simply look that the side of a time fuZe for a spelling lesson. The cover of a fuZe package also provides some enlightenment to us too slow to pick up on the obvious hints.
'Nuff 'bout that!