You need to locate a Mitsubishi 4M40 turbo diesel engine. I see them on ebay from time to time. The 4M40 is a direct bolt in for the most part. It should bolt up to your current tranny and your tranny should be more than capable of handling the torque of the 4M40.

Spence
1985 Mitsubishi PU 2.3 Turbo Diesel, 13" lift, Watercooled turbo, 4D56 Head, Atlas II,Fox Coilovers, Elockers,

1983 Mitsubishi PU 2.5 Turbo Diesel 4x4, fully restored

2003 G500, sliders, beadlocks, roofrack, ladder etc.