Quite a concept to get rid of material...Apparently the "backpack" is the power unit to give power to the chain on the dozer...
Another interesting unit...K Tec 1245 ADT out of Canada..Employs a 44 yd scraper and a 40 ton ADT...It would make for an interesting model...6 wheel drive
http://www.ktecearthmovers.com/index...d=65&Itemid=70