I can give you some idea, from a hobbyist perspective.
I pulled out an MV404 engine and 5 speed, pretty much the same size and weight as a 6.9.
Took me all day, working on my own. Not too hard, just a LOT of heavy stuff to move.
Two guys in a shop, with the right tools, could do it in a day. That's 8 hours.
It's the install that takes time, and all the things that crop up.
To change to the DT466, I've had to make a lot of little adjustments.
Cut out the doghouse, new place for the accelerator pedal and cables, electrics had to be
carried over from the DT to the old firewall, then spliced internally.
New holes all over the firewall for stuff like the tach cable and doghouse bolts.
Some stuff lines up perfectly. Some not.
It's taken me longer than anticipated, but I'm almost done.
I'll drive it in a few days
Did you provide a donor vehicle, or was this parts sitting on a pallet? Makes a difference
having everything available and not having to run around looking for stuff.