Thanks! The primary purpose of the tractor, as I (take a look at thel link) will call it, is to haul water around - anywhere from 3,000 to 5,000 gallons. It will be an agricultural vehicle. The water tank will be removable, and the moving platform can be used for other things. The front will have a front loader, the rear a backhoe, with a 3 point hitch and pto for other attachments. First round of brain picking says that a 6bt would be adequate, but they are 37" tall, put out 200 hp and 420 ft lb of torque. Subaru makes (made?) a flat water cooled turbo diesel but they are fazing the engine out - it was also never distributed in the US, so parts would be a nightmare to come by. I want to stick with diesel because of the better fuel consumption numbers and because one of the most important purposes of this vehicle will be in fire prevention. I live in the desert and wild fires spread across the flat plains like a bullet. Diesel is a little more stable than gasoline in high temperature situations.
I was thinking that 2 of the 1.9 tdi engines might match the 6bt numbers - a little short on torque - but would be 60% of the weight. Height is one of my main issues here. I want to keep the center of gravity as low as possible.