Personally im running a coppy of a Rocky Mountain gear box brace, 3/16th plated frame, and 1/2 of the T&T Steering Box Brace Kit.
I would deffentally go with some kind of frame sandwich plates, to me 3 bolts into sheet metal isnt what I want holding my gear box on. If you do choose to go this route get the plates before you make the bumper mounts. Because youll want to make the bumper mounts strech along the frame, and the extra 3/16th plate will be right in your way. Its a lot ez'er to make the bumper mounts around the sandwich plates. Just a tip from someone whos had to bend his bumper mounts 2 times now because of it.