well no updates but I did pick up a key piece to the puzzle and a bit of a motavator, I found a 1/25 scale autocar dc9964b model. I will use this kit measure and scale up from to make my 1/10 autocar dump. here is the kit I found hiding at the local hobby shop
I may redo my box sides now to make it look more like the one on the model and match the time period.