Yes it is a direct fit.
NO
The Express version of the 870 Remington is normally either 12 or 20 gauge. Gauge desigantion is marked on the barrels left, rear end.
Yes.
12gauge magazine cap fit on a 2ogauge 870 mag cap
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.
The W ahead of the serial number indicates that your Remington 870 wingmaster was made in 1972.
The 870 is a pump action shotgun. The 1100 and the 11-87 are the two standard Remington semi-auto shotguns. In 2008 Remington introduced an 870 with Pheasant and Duck engraving and a semi-fancy claro walnut stock. This was a premier dealer gun. http://www.remington.com/products/firearms/premier_dealer_exclusives/model_870_wingmaster.asp
No.
No. The 11-87 has a recoil spring & tube in the stock, the 870 uses a single bolt.
Serial 718943w
Impossible to answer without a serial number.