I love the idea of a new crate Diesel (R2.8) but it's a $9000 motor that makes 160HP and 267lb/ft. Then add mounts, cooling, exhaust, trans adapter, and fuel pump and you're pushing $12k. I think it's a little weak for a >4500# GWag. To me the R2.8 is great for CJs, YJs, and TJs but a FSJ needs more torque/power.
You can do a pretty sweet 5.7L Hemi/trans swap for half that and end up with much more power and torque.
I think your 4BTA is better suited for our big trucks and it would be pretty awesome.
79 Cherokee Chief, barely runs
(Cherokee Build Thread)
11 Nissan Pathfinder Silver Edition 4x4
09 Mazdaspeed3 Grand Touring