Joshua - they can be 'modified' to work, but there's quite a bit of work involved. the 1187 will need a larger channel inside the stock for clearance of the recoil spring set up among other modifications. Newer 870 stocks don;t require as much work as the older ones. My opinion is just get a youth stock made for the 1187, to save yourself a bunch of work and headache. However, if you're the 'handyman' type, there are plenty of articles and discussions available on the internet to guide you through the process. Check Flea Bay for starters, if you elect to buy one.

Joshua, No. The 11-87 has the tube for the spring that goes through the stock. The hole in the end of the 870 stock is too big too deep to allow the 11-87 stock bolt to tighten up and hold the stock 870 stock in place on the 11-87 spring tube.