tndonor

I can only speak of the Cummins options as that is what I have experience with. I had a 1980 J10 that had a cummins 4b. Fit no problem. I currently have a 67 m715 I am putting a Cummins 6B into. I will run an electric fan to keep the stock dodge hoses. But it fits. I am going to keep the intercooler so Ill trim the front valance to recess it in there. The main question is are you willing to alter the stock panels, if so anything is possible.

As for a constant duty engine (generator, pump, etc). They are designed to be effecient at a given RPM. They MAY have a different camshaft which if spun at road speeds for prolonged periods can chew up cam lobes. Also even more important is the injection pump. If it is a load governed pump, IT CANNOT BE USED ON THE ROAD. Nor can it be modified for road use. The throttle is load dependant and essentially the big skinny pedal in the floor is in the pump itself.

Again, this is related to Cummins. I imagine that other motors are of similar design but I cannot speak for certain.

Hope this helps