You may want to check out this section about "what is it like to own a diesel" which compares swaps from USA-available Diesel Engines into Land Cruisers versus factory diesel swaps.

Most of this information is courtesy of Ken Dahlberg, who has kept a record of diesel engine related conversation from the LCML.  Likewise, Morgan Fletcher (New Window will open),  Rob Mullen (New Window will open) and others have unknowingly contributed to this page.

General Information and Thoughts
From the information I've gathered I've now come to the conclusion that the Isuzu 4BD1T is the best swap for a Land Cruiser.  It fits easily, has reasonably impressive power output, and has most of the best available features for a diesel engine with little modification required to the Land Cruiser.

Impressions of the 4BD into the Toyota Land Cruiser (lengthy read)

Statistics and Conversion Information:

• The 4BDT is AKA the QD100 - same motor, sometimes w/o turbo, used in non vehicular applications. It's in Isuzu and GMC cab-forward trucks and vans. (Avoid industrial applications in automobiles, they have different output specs, fuel pump settings, and are not designed for on road use).
• The physical size of the 4BD1T Isuzu motor Info from engine plate is

116 hp at 3000rpm 235 cu.in.
Engine size- front of fan to rear of engine block 30 1/2" bellhousing front to back 4 1/2" height 31" Width from outside to outside of everything 26"
And it weighs 715 lbs.
• The 4BDT will require an overdrive, 1:1 high gear won't cut it. This is because the red/line peak RPMs are in the 2500-3000 range. Though the peak HP is 3000 RPMs, you will probably never want to take it about 2500 rpms.
• Isuzu makes an adapter that allows SAE #3 bell housings to be used therefore you can use GM trannies. However, the Isuzu part is now discontinued (as is the 4BD1T, it's now been replaced with the 4BD2T engine (which has higher output & is electronically controlled).  Otherwise, the bellhousing pattern of the Isuzu 4BD is a Sae #3 (same as a Chevy 350), but with the bolt holes rotated about 15-20 degrees.
• Best solution is to go to an "annular" throw out bearing that doesn't use a clutch fork, as there isn't room for clutch cylinder & starter on the left side.  These are found in Jeeps and Peugeots. 
• 4BDT features integral, gear driven PS and vacuum pumps. You might also want to check this page on (devices for) producing vacuum.
• 4BDT / transmission junction needs to be more forward than SBC or 2F. That plus need for overdrive make the NV4500 a natural pick.
• 4BDT in USA Specs are 12 volt.