The current Henry...
...Arms product is more of a copy of later Winchester models and they have no connection to the original Henry rifle. The new Henry does eject from the top (as do most lever actions) but has a loading gate on the side of the receiver, a feature that does not exist on the orginal Henry of 1860. In the calibre you are looking for the only model offered is the Big Boy which only comes in a 20 inch barrell, but is octagonal. It resembles the Winchester 1866 Yellow Boy. Have not a clue as to how well they handle BP, since I've never seen anyone use anything other than smokeless.
You seem to be on the same path as I, following a progression of C&B, to cartridge to reloading. I'm just a little ahead, started reloading 38Spl and 44Colt in January for my Mason Richards conversions. Next acquistion is a Uberti 1858 Army conversion in 45LC, so I can start reloading that round. After that I will add a Uberti Henry rifle in 45LC, but that will have to be after the 1st of the new year. The plan after that is to stop buying cartridge and go back to buying C&B when the need arises to quell the BP urge for a new toy.