Re: 1867 Remington .58 caliber
Maybe I am mistaken, but AFAIK the Model 1867 Remingtons (there were two models, a Navy contract carbine and a cadet rifle, as well as a Navy pistol) were all made as cartridge rolling blocks, not conversions, and all in .50 CF. There were some conversions, but they are pretty rare. (Unlike most conversions, the Remington conversions pretty much scrapped the original rifle muskets, keeping only the stock, which was cut in two, and the barrel. The rest was replaced by the rolling block action.)
The Jukar is a modern gun, not really a repro or a replica, just a new-made gun.