Wasn't that difficult. The bottom rear of the reciever has a tang extending out so had to cut away some material for that and the extension on the stock that fits into the reciever had to be trimmed some as well as reducing the amount that it actually extended into the reciever.
If you remove your factory stock and compare it to a 870 stock you will see what needs to be done. The most extensive part of the mod was cuting out for the rear tang.
Just used a dremel.