JMO, put the time and money into a HDT. You're not gonna like that MDT after using it awhile. The DT466 is a good engine, if you dont mind leaking cylinder o'rings and injectors. It will run forever at 210 hp, 300 would be ok, however, the transmission is probably not rated for it. The chassis will be loaded closer to max than an HDT, meaning not as much breaking power and the lack of a "real" jake break becomes a big deal. Lots of folks have built on a MDT chassis and been dissapointed. I've not heard of anyone building an HDT that thought they needed more power, breaking, or load carrying ability. YMMV