Good Morning dive585, I think what you are looking for is one of the 2000 amp welders built by Lincoln or Hobart. Each built a unit powered by Detroit Diesel 671 engine. These are still around and the ones I have seen sell for 15000 to 25000. Quite heavy machines and give a lot of trouble. The Lincoln was sold through Nelson and painted red. The way I understand it, Lincoln will only build these now in quantities of about 5 or 6 and Nelson priced them at about 50000 each. Miller did not build such a large machine. There are some other games you could play if you have the time, money, patience, etc. - connecting multiple diesels in parallel, for instance. Millers are particularly suited to this type of use. We have this type of equipment in stock as well as the gun and controller/timer.
The more popular way of attacking this problem, at least in our part of the world, is to get a conventional diesel generator, say about 150 kw, trailer mount it with a conventional electric stud welder and go to work. This has the added advantage of allowing dual gun use if you choose dual gun stud model. All this type of equipment is readily available. If any of this helps, email anytime.
BTW, for anyone using this type of gear, we have some of the 671 Detroit engines left.