The Freund "improvements" were the breech block was made to tip. As the action was closed the block would cam forward to press the cartridge into the chamber. Note the screw on the side above the word Boss, this held the wedge that engaged the bevel on the top of the breech block. Other details aren't as important. The breech bock and cam plate are in the top right of this photo.
Blair, the other parts can be bought from Taylors. Pedersoli parts won't work. These actions still need some machine work on the extractor slot and lever spring opening. The corners inside the breech block opening is radiused so that can be squared up or the breech block corners rounded to match. As such no FFL is required. I miss stated before there isn't a trigger plate but there are screws, bridle, receiver, lock plate and lever. These require machine skills to finish unless you are very good with files and understand how to build a 1874 Sharps! I have no dog in this hunt, I only post tis as I've seen people wonder about building their own.