Here is the solution to capping an 1858 without modifying the cylinder:

using this capper :

Unfortunatly, I don't believe that capper is made any more. I think it was maybe made by Uncle Mike's or CVA 25 or so years ago. If anyone knows where I can get a few like this, or even who used to make it, lemme know. In case you are wondering, there is a narrow slit about an inch long on the back side as well, which allows the forward-most part of the tube to be pinched down. That holds the front cap in the tube.
Since I don't know where to get more of them, I stared at a Tedd Cash capper awhile and came up with this idea :

using this modified Tedd Cash capper :

It still needs a bit of tweeking, and the best bet would be for "someone" to make the nosepiece from scratch designed especially for this purpose. (Scott from Cash Mfg. Co ... hint hint

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The tang on the original design would go away. A proper nose piece would be necked down as soon as it clears the tube on all four sides to form four separate fingers. The 4 springy fingers might want to each be curved to form a circle to better hold and guide the cap.. The fingers would flare outward slightly at the forward most position. This would allow the capper to be loaded by simply pressing the capper over the top of a bucnh of business-end-down caps.
Rick