NO! The 1187 barrel was for remington shotguns,the auto-5 shotgun is a browning shotgun.
No
NO
It will fit on the frame but the action will not function with 3 inch shells.
Probably not but call your local gunsmith
no
No, the Remington Model 1100 stock has a hole (recepticle) through the inside of the stock in the pistol grip area to accept the action spring tube. The Remington Model 870 stock has no need for this hole so the 870 stock will not fit on the Model 1100 action.
No
AFAIK, no.
yes it will all you have to do is to take it apart
no but it will fit a mossburg 500
No there are ways, it invalves drilling holes to vent gas witch operates the gun.