My guess would be that you don't need a weight distributing hitch at all. The hitch on my pickup had a stamp on it that said it was good for a 5000 pound trailer without weight distribution and a 10,000 pound trailer if I used a weight distributing hitch.
If you want to use the WD hitch you have, you can buy replacement shanks with a greater drop. There are several on-line retailers who sell these.
2012 New Horizons 36' Travel Trailer, Front Kitchen
2008 Dodge Ram, 6.7 liter Cummins Diesel, 4WD, Quad Cab