The manufacturer states Hogue Remington 870 20 GA. OverMold Shotgun Stock Kit is only for 20 gauge 870's. Hogue Remington 870 20 GA. OverMold Shotgun Stock Kit may work for a youth model 16 guage but I recommend contacting the manufacturer to confirm compatibility.
The Hogue Remington 870 20 GA. OverMold Shotgun Stock Kit will not fit a Remington 1100.
This Hogue Remington 870 20 GA. OverMold Shotgun Stock Kit is designed for early 870 models which means you will need to increase the bolt hole diameter in order to fit it to a Remington 1100.
I do not see any spacers that will be compatible. However, a thicker pad would also do the trick. Here is a link to a possible item. https://www.opticsplanet.com/sims-vibration-laboratories-airtech-slip-on-recoil-pad-one-inch-large-black-1055.html
The buttstock may fit but the forearm will not.
The stock should fit the Stevens 320 12ga and 20ga shotguns however the forend will not.
Item 08717 and item 08217 are both 14" LOP, item 08737 is 12" LOP. Unfortunate Hogue does not have spacers for their stocks.