2008 F450/MS TA Shackle Setting or what?

[Mikey]

Rig: 2008 F450 Dually - 2007 MS36TK3

I have minimal clearance between box and bottom of "gooseneck." (under the bed/bathroom) 4" - 5". I've almost put holes in it twice! Thank goodness for a bit of flex in the fiberglass and a great "spotter" - Maureen.

Shackles on TA 17.5 wheels in middle location. (could raise one hole)
TA pin box in top holes. (could lower one hole)
Reese hitch at lowest adjustment. (could move up)

If I adjust just the pin box or the hitch, I'm going to put extra weight on the rear axle. I want to keep the trailer as level as possible.

I know a couple of you have a similar "rig."

What's the best way to increase the clearance?