Here are the specs...
Engine RPO Codes: LH6 ('C' series, with EGR) and LL4 ('J' series)
Displacement: 6.2L / 379 cu in
Bore x Stroke: 3.98 in × 3.80 in (101 mm × 97 mm)
Block / Head: Cast iron / Cast iron
Valvetrain: OHV 2-V
Horsepower / Torque (at start): 130 hp (97 kW) @ 3,600 rpm / 240 lb·ft (325 N·m) @ 2,000 rpm
Horsepower / Torque (at final): 143 hp (107 kW) @ 3,600 rpm / 257 lb·ft (348 N·m) @ 2,000 rpm
Horsepower / Torque (army): 150 hp (112 kW) @ 3,600 rpm / 260 lb·ft (353 N·m) @ 2,000 rpm
Max RPMs: 3,600 rpms
Idle RPMs: 550 + or - 25
And keep in mind this IS NOT the infamous 350 diesel that Oldsmobile tried. This was built from the ground up as a diesel for use in the military pickups and blazers, then adapted for civilian use. What's not listed is the ease of instal. It uses the same motor mounts as a SB/BB Chevy, and weighs in just under a BB. These were made for durability, longevity and mileage. And out of the suburban I picked up, it was getting 18mpg on average! So in the YJ, weighing about 1/3 as much, should get somewhere in the neighborhood of high 30's maybe low 40's.