I am running a Cummins "C" in a 95 FL 70. So, I can speak factually about this engine. To find more about the Cat 3126 you need to refer back to this bulletin board. The truck I bought had been abused big time. Although I had the truck dyno'd at time of purchase I was not aware of the extent of wear and tear on the engine. At about 300,000 miles I took the rig into my Cummins dealer in Buffalo, NY. After some discussion and some soul searching, I elected to have the engine rebuilt rather that go into debt on a new rig. I had a complete in-frame rebuild on the engine and a rebuilt turbo installed. The cost was $6,500 all inclusive. Try to get a CAT rebuilt for anything near this price.
I have put about 120,000 miles on this rebuilt engine and it purrs like a cat. (Pun intended). This engine is rated 175 HP and I recently pulled 12,000 net (30,400) gross up the grades on I-77 from SC to OH. Needed to drop down to 5th from time to time but I outran a number of the 18 wheelers up these grades. (What a great feeling)!!!
So, the big advantage as I see it is the maintainability of the Cummins. I also wish to pile some praises on Cummins Northeast in Buffalo for the fine job they did on this rebuild.
Drop me an E-Mail if I can give you any more info.