I'm on the far east side in Sidney. I go thu Missoula a fair amount, but seldom make it to your area. If i was gonna keep the truck, I would consider doing the 6.4, but It's a flipper. I looked a little closer at the newer motor, and only thing I notice is the coolant cooler between the oil pump and filter. The dealer here has one of the "Noisy" 6.4 takeout engines that I've been trying to get. That would go into my backup towing rig. Hard to beat my '05 Cummins for towing, tho. Jim
I love this engine in mine much better than my old 99 cummins, it tows about the same, gets the same MPG but the fuel and oil changes are cheaper and I could replace the entire engine for about the price of replacing the injectors in a cummins. I got a 6.4 BGE short block, eagle heads, cam, intake... and it tows better than a stock 6.4 truck and better MPG because of much higher cylinder pressure from the compression bump, earlier intake closing, less overlap, no EGR. A 5.7 in a 2500 4x4 is kind of a dog, I had a 2014 with a 5.7 and it shifted twice as many times on a trip as this one does.
That oil cooler is super easy to just unbolt it if you don't like it and screw your old nipple in the block. If you want to run it and your old engine didn't have it just leave it there and run your heater hose to it and a short piece back out, takes 5 minutes and a couple feet of heater hose to add it to a truck that didn't have it. I eventually put one on my 6.4 truck and it gets the oil temp up faster and keeps it from getting as high, I think of it more as an oil temp stabilizer. Your 2500 has plenty of space for it. You can even just leave it there with no heater hose going to it and it won't hurt anything but won't carry away much heat with no coolant flowing thru it.
One more thing I would look at is possibly the later engine might have a spacer ring in the back of the crank like the car engines, remove it if it has one but I just don't know if it does or not.
