They make adapters just for your I-beam Trailer....lemme find a pic and some links....BRB
Back.....
Here they are
Tongue Pole AdapterYou're hitch dealer, or local RV store should be able to dig up something for you on these.
*edit*
If you still want to sell it, shoot me a PM with your address so i can get a shipping quote. I could use a WDH on my S10. The little 18.5 isn't terribly heavy, but the springs on the truck aren't terribly strong either, and I could use the hitch when pulling my Xtreme on the car trailer.....however I'd much rather see you get some use out of your $400 of steel than sell it to me!