#1 - DON'T just drill and tap the tube.
I've talked with the mechanical engineers at work and their isn't enough thickness to support the threads. The tube would need to be something like 3/8" thick to handle the stud.
#2 - I spoke directly with Bushmaster when I bought my Vmatch. They DO sell a kit for adding the stud, and readily admit that the standard swivel negates the benefit of the freefloat tube. The correct kit is the Harris #5 bipod adapter, same as the standard handguards use.
#3 - attachment - you mark & drill the clearance hole for the threaded insert in the studplate. Place a thin sheet of metal between the barrel & the handguard to protect the barrel when the drill pops through. Take some needlenose pliers and insert the studplate between the barrel and handguard, aligning the stud with the hole. Insert. If the stud stick through, the square washer (use on the outside) will bottom out and you won't be able to tighten it. Either grind a little off the stud, or countersink a relief in the square washer. That was my choice, easier to do. Only a few thousands is needed. Apply loctite and tighten the stud.