Well...just off the top of my head...

5.7L Hemi swap is fairly do-able, lots of parts out there to make it work.

Overdrive transmission...and then 4wd...there's where you will run into problems.

OD trans is longer than a 727, and won't mount the same. Transfer case from an 03 has the driveshaft on the opposite side, when compared to the t-case in the '77. Won't line up with your front axle.

5.7L Hemi swap to the 727/NP203 t-case is possible, but would not get him the OD trans. Biggest issue with the M880s...geared VERY low. He's probably looking for SPEED over power, and with those low gears, those heavy M880 trucks don't go too fast (I had a '77 M880 318-2V, I know). Mine would PULL very well, but highway wouldn't go much over 55-60 at best, and would get around 4 mpg (until I tuned it up, but still wasn't very good!)

Good luck!

JS