The only good part I would see about buying a irrigation pump motor, or one out of a piece of farm or construction equipment is that non automotive applications almost always came with the water to air intercooler. (if ordered with it/equipped with it at that power level) as long as it isnt too tall, that would eliminate the issue of locating an Air-to-air intercooler in the cooling stack.
dieselcash is definitely correct, you would still need all the automotive accessory brackets.