Well for any iron over 7500lbs Diesel would be the choice without question. There is NO gasser that will hold up for the long haul. Being a 1 ton ford pickup is already tipping 8000 LBS I would assume this rig will be well equiped as well. The older common rail cummins is much easier as far as electronics goes. Less computer and more mechanical means of adjustment. How they mate a Ally with the Cummins is by a custom plate. I would think the hardest fitment will be the Front and mid motor plates and having room for them. Since its an older piece of iron it sholdn't be a problem. I guess when I was reffering to the common rail it was also the mechanical injection models of the cummins. Its what all the serious fabricators and racers are using. Easy to find , cheap price, and lots of info and parts available cheap. Plus there is NO worries about whether it will last. The cummins is what most UPS trucks use, just a 4 cyl version, alot of pop and beer trucks run the cummins too. Its by far the most proven motor and most widely used with the most applications. Since the intro of the cummin 6BT5.9 in 1978 Ford and GM have gone thru 9 + full size diesel powerplants, this doesn't include the Dmax nor any of their OTR diesel power plants for the bigger trucks. And still today none have produced a package that has even come close to the power and reliability of the single Cummins design. Now the Dmax is a great engine and will be slightly easier to marry together electronically, but if your not dead set on the Dmax ,research the 2 more. In fact theres articles of the Cummins in a 66 ford bronco. A Dmax in a 1970 C-10 pick up, and a powerjoke in a jeep wrangler. What ever you do, do as much research as you can. Because I can gurantee you'll be doing plenty during the build. You WILL become one heck of a fabricator and engineer by the time your done, but thats nothing compared to the pride you'll have of owning a piece of Iron like that.