NO! The 1187 barrel was for remington shotguns,the auto-5 shotgun is a browning shotgun.
no but it will fit a mossburg 500
No there are ways, it invalves drilling holes to vent gas witch operates the gun.
Without seeing it, almost certainly not.
It will fit on the frame but the action will not function with 3 inch shells.
You will need a good gunsmith. The information you seek is not readily available in published material.
Yes they are interchangable.
You will need a slide/ barrel bushing that will fit the barrel you want to install.