Sorry, no answer from me, but I would like to know the answer to this question as well.
no
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.
NO
12gauge magazine cap fit on a 2ogauge 870 mag cap
No. The 11-87 has a recoil spring & tube in the stock, the 870 uses a single bolt.
You will need a good gunsmith. The information you seek is not readily available in published material.
Yes, The receiver pins are the same as the Remington 870, so any stock that will fit the 870 will fit the 7400
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, Winchester 1400