Hey Miker12, something has been bothering me, so I came back and realized what it is. That your first pic has a folding rifle stock and the two others, don't.
Big difference (I THINK) putting a short pistol barrel on a stock capable of being full length with a folding stock,... without a stamp. Which I assume is the bases of your quest. I am going to take an uneducated stab at this (since no one else seems to want to be helpful) and say,... even if the first pic, with the folding stock and short barrel is manufacturer/factory issue, NO, you can't manufacture a pistol with a folding rifle stock, even though it is obviously a C&R piece, that is made exactly to what you seek to do. I believe you could get away with replacing the folding stock piece with another manufacturer/factory issued correct action, but that is obviously not your goal.
I believe,... it is one thing for a licensed manufacturer/factory, to do what you want to do, compared to a civilian changing out the original action/barrel to a different type. But, as I prefaced,.... this is a wild stab!
As to the other two pics, they seem to be factory made pistols,.... if they are manufacturer/factory original pistols, I see no problem changing out those pistol barrels, to a different pistol barrel, or a rifle barrel, if you wish. But, I believe you would run into basically the same legal problem if you mounted a folding stock , on either one of them.
We have a shitload of FFLs on this board and I don't know why they haven't chimed in,... maybe they just haven't seen your post.