longcaribiner,
The were many period conversions of the trapdoor to those cartridges, and others sharing the 45-70 case head and length.
Even some "sporterized" conversions.
I have seen two, both in 40-65, and the stock on one was not unlike a modern stock. It was an English conversion. I wish I had photos.
There really is nothing new, just old ideas recycled.
By the way, my 50-70 was made from an italian 1841 Jager or Mississippi Rifle, (see above photo)