If the auto was a 700R4 or Turbo 400 from the 6.2 vintage, that would be as easy as the manual. Trying to get a 6.2 to work with a more modern 4L60/80/85E models....not so fun.
Wouldn't be very gutsy, but could do pretty good mpg wise and of course it's a diesel, so it's cool.
If you have emissions in your area, you may find it to be a bad idea. I know up here a few years ago, you could convert a gas to diesel however the motor had to be of the same vintage or newer than the truck it was going in. We no longer have emissions tests and such, so no problem any more, but check local laws prior to getting too excited.
05 2500HD CC LB LLY, 4x4, 3.73s 235/85R16's, webasto cab heater, to keep it warm.
03 Buick Rendezvous - When you average over 80 miles per day driving around, you need one of these.
85 K-5, 6.2, SM465, Rockwell T221, 1 tons, 36's. More goodies to be installed as time and money allows.
82 K20, 6.2, SM465, NP208, stock except for bed rack, snow plow, and glow plugs are on a toggle switch. It works great for plowing!
72 Postal Jeep - Yet another project