The drive train from your ram would be a great swap to my 77 Midnight express/Warlock clone.
one thing with using the stock PCM, in an older vehicle is SOMETIMES with the new vehicles it has the PATS system, where you need the "chip" in the key for the thing to start, that can be a headache to overcome in some swaps.
The install kit Mopar sells is for the outside(engine bay) not for any gauges(except the sensors required by pcm to run the engine) Its the engine harness, with fuse block, and relays.
So for the gen 3 to run in your car, AND have the dash gauges work, you probably have to "T" into every sensor, and add the OE sending units, so one signal goes to Gen 3 Hemi PCM, and one signal, via your "T" to the dash gauges.
You can get around this with a modern set of aftermarket gauges, (that run on same voltage as the factory gen 3 pcm signal)
Or to run a Diablo/Tunner via the OBD2 port, the screen on tunner can be set to act as gauges, but not as cool as dash gauges.
For install of just the Gen 3 engine, in your Coronet, they make engine mount kits, for it to bolt right in on stock K frame.
If you are using a modern automatic trans, as what is in the ram(minus the transfer case)
then I am fairly certain major torsion bar/ trans crossmember surgery is required.
I have always drew the line at hacking up my car, not do to fear of welding, but I just dont wish to cut up my car.
So as far as a modern automatic transmission going in our B bodys, I know very little in that area.
I did fit a 1998 5.9 V8 and 46re trans in a 73 Challenger, and I just did some minor grinding on the transmission case and hammer work on tunnel, and it fit fine, I had to make a new transmission mount, but didnt have to cut anything on the body.
I know that was an E Body, not a B.
I have been told,or I have read, but I don't know if its true, that an E body is wider and the engine is mounted a touch forward then our B bodys