You will only have to drill 1 hole in your stock-the buttstock. The front swivel stud should be the kind that's sandwiched between the barrel band ends. Remove screw from the barrel band, spread barrel band, insert swivel stud end between the barrel band ends, replace screw back into the barrel band.
The best way to locate the drill hole in the buttstock is to make a homemade jig to center the hole precisely in the bottom of the stock. You can easily do this by drilling a hole exactly in the middle of a piece of either 1.5" or 2" angle iron from the inside. Then invert the angle iron so that it's sitting on the outside of the bottom of your stock. Simply use a drill bit the same size as the shank of the threaded part of the swivel stud and drill it to full depth of the length of the stud. You can then thread it into the stock, remembering to press down slightly to start with.