A friend of mine -- ok its me -- has the complete bottom section irons of an original barbette carriage that during the war had a 6.4" CS Brooke on it. It was recovered legally on private property and is sitting in a (very affordable) pile awaiting restoration. It is available, but I passed on parting it out to a National Historic Park a few years ago. It would've been cheaper for them to buy some of the parts than have those parts remade on their super expensive repro carriages.
Since then, a couple people involved in this Pee Dee recovery have crapped on it saying the one I have out of the Mobile defenses is a "Yankee" carriage. They whisper this like its a huge secret that these big barbette carriages were designed prior to the Civil War so essentially are common to both sides. The truth gets in the way of profits from selling carriages made of old log wood recovered out of the very same waterways these Pee Dee tubes rested in. I have no idea, nor do I care enough to ask, where the wood came from for these carriages, but it wouldn't shock me at all if some self interest is not partly behind this mis-"carriage."