Yes both the 11-48 and the sportsman 11-48 are the same gun. The only difference is the sportsman came standard with a plug to limit capacity to 2+1 to comply with hunting laws.
You will need a good gunsmith. The information you seek is not readily available in published material.
You have answered your own question.
NO! The 1187 barrel was for remington shotguns,the auto-5 shotgun is a browning shotgun.
no
no
AFAIK, no.
no but it will fit a mossburg 500
No there are ways, it invalves drilling holes to vent gas witch operates the gun.
IF it is possible, stick with Remington parts.
700 ADL Long Action
Without seeing it, almost certainly not.
It will fit on the frame but the action will not function with 3 inch shells.