I wouldn't have mounted lower link to the stock crossmember, I think you will bend it. That one link sees more force than any of the others, its one of the disadvantages of a 3 link.
Also, I would use 6 bolts to secure the two "upper" link mounts (instead of the 3 you're using now). I would add 3 more bolts above the 3 that are there. And you don't need to drill big holes in the square tube to get to the bolts, just install the center one first.
Out of curiosity, have you seen the
3 link calculator (first link on this page)?