I have several 870's and 1100's, the barrels and forends can not be swapped between them. Don't know if the stocks can be swapped either.
Personally, I would keep the 870 for home defense. I have an 870 Police Magnum and it is my home defense shotgun. The 1100's and Saiga-12 stay in the safe for HD.
Yes, you can short-stroke a pump and have issues, nothing mechanical is 100% perfect.