This is an idea i had floating around in my head, but due to a lack of bits hasn't happened yet. Its a great truck Frank, but have you considered moving the pivot point of the lifting mechanism to the back wall of the cab. I think this would allow the arms over the cab to be shorter and then when the bin is in raised it wouldn't be so high up in the air.
You may want to rethink this being the final version, because I may have solved your container-dumping problem. http://fallschurchtimes.com/wp-content/uploads/2010/03/frontloader.001.jpg Here is a link to a picture of a top-loading truck, and as you can see, the top of the collection container is raised higher than the cab, and extends to the front of the cab. You may want to try this technique, I think it would solve your problem!
Awesome job on this. I tried months ago to make a 6 wide dump truck with the collection arms or whatever they are called and just couldn't figure out how to make it without it looking real bulky. It looks like I was using the wrong parts. Nice job