Hi LJW!!
I personally, from a Gunsmith point of view, think it would be an unwise project. The frame would have to be cut apart at the Carrier Block mortise, welded back up and pass proof. That's the easy part.
Everything else has to be re engineered. Breach block too long, links too long, lever throw too long, the list goes on. Just to make the frame about a quarter of an inch shorter?? and you'd still have a cartridge that is too long to be correct (.44 Colt). .44 Russian would be much closer. With a simple set screw (cartridge stop) in the carrier block and corresponding relief in the side of the Breach Block, the rifle will run .44 Russian just fine.
I realize your a stickler for authentic, but in this case, Obsessive Compulsive Disorder may lead you down a dark and Rainey path. DONT GO THERE.
Relieve your anxiety and sell me the .44 Special chambered Iron Frame Henry instead.
Ever hear back from the folks in the East who were making Henrys?? Or has that trail gone cold??
Coffinmaker