Heh - a late welcome to ya, that's a dang nice build you have!
I have that same rear rack and tbh - I'm really not it's biggest fan although it looks cool (no offense). I've just never been happy with it's side movement no matter how tight you had it. Of course if people would stop grabbing it to move my bike (myself included lol)... I did drill it and add vertical supports from another rack, obv it doesnt need the added strength - but it did make it rock solid and stopped all movement.
Have you considered the "hide-away" rear fuel tank & rack? It's on my "to do" list lol
ThatsDax has 'em if yer interested.