So, here's my input: same as before, go Cummins if you already have the engine, mounts and adapter.
It's going to cost you some coin if you can't do at least some fabrication.
You need a body lift or be able to work the transmission tunnel area. A BFH can get it done. BFH more of less makes a mess, but it's functional. depening on your accessories and placement, you may or may not need a cowl hood.
The cummins will clear the IFS, but not by very much. A front suspension drop kit makes it more "comfy".
The 4500 will bolt up to the cummins with the right bell housing/flexplate assembly.
Since your truck is a diesel, you gauges will work fine. Us ethe 6.5 sensors in the cummins and they work fine. The tach works off the alternator, so either swap the gm one on the cummins or tap a single phase of the Dodge alternator. The speedo is driven by the VSSB module int he dash by the PCM. If you keep the GMtransfer case, you keep the VSS which feeds the VSSB. It gets a little dicey if you have the pushbutton transfer case, but hte lever case is just fine as is.
The cummins just needs a 12v + and it will run.
You can pull the pcm out at that point as it won't be running anything. Pushbutton xfer case I'd have to look at the wiring diagrams first, I seem to recall some interaction between the PCM and the transfer case shift module. Can't say for sure off the top of my head.
With the cummins and 5 speed, you will be ditching the engine oil cooler and there wasn't a transmission cooler to start with. It may be possible for you to sneak a 1st gen intercooler in there with those items gone. With out the AC condenser, it should fit easy peasy with a bit of rad support cutting.
Driveshafts aren't an issue if you keep the 4500 and transfer case.
The exhaust will need to be redone.
The fuel system is insufficient to effectively feed the cummins. It can work, but it won't be happy. The GM lift pump needs to go. They're sketchy at best. I'd use the dodge one before the GM. Walbro FRB10 is a decent choice. If you want to spend 300-ish bucks, you can get a raptor 100 kit with 1/2 push-lock line that replaces the GM system. You will need a 5-ish micron filter, a racor will do fine.
If you have the p7100 injector pump it's pretty rbust, the VP44 is kind of delicate and you need a good "flow on fail" lift pump.
If you're using a bread truck adapter, it will tilt the engine to the left. It's the way they are with the 4BT in the bread truck. Clearance with the turbo is the issue with the tilt if your turbo manifold is the low mount.
not sure on the PS hookup. I can't remeber if guys use he cummins pump to drive the PC/hydroboost or adapt the GM PS pump to the cummins.
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AC, if you hook it up, needs to be fabbed on. Pretty sure I remember it not just "bolting on".
That's about all I can pull off the top of my head...
By the time you're done, even with the parts you already have, expect to have at least a couple grand into the swap.
considering the truck you have, I would expect anywhere between 15-20 mpg. You rear ratio will have a lot to do with it. Obviously, deeper gears means less MPG....
