Bob, I don't know if you have the fifth wheel figured out for your build yet, but I just found this one for mine (which isn't nearly as progressed as yours is).
http://www.ebay.com/itm/1-14-5th-Whe...item27dce05390
I ordered it about two weeks ago, and just got it in today. It's all metal and pivots both forward-rearward, and left-and-right. The release handle unlatches it well. It comes with a new 'mushroom' for coupling, as it is somewhat smaller than the Tamiya one. I tried making my own out of Tamiya bits, but was never happy with it. This one is really nice, and I'm glad that someone finally made one. Now, if they will only make a sliding fifth wheel.... -Mike