This page compares available diesel engines to provide the most suitable application for your conversion.  For 1-10 noise statistics, 10 is the loudest.
 

Engine	Size	Direct Inject?	HP	Torque	Bolt Pattern	Red Line / Governed RPMS	Noise & Vibration 1-10
Cummins 6AT	3.4L	No	~132	~230	Chevy w/ Adapter plate	3500	4
Cummins 4BT w/ Bosch VE  Fuel Pump	3.9L	Yes	107	~300	SAE #3 / Chevy  (both)	2500	8
Cummins 4BT w/ Bosch P1700 Fuel Pump	3.9L	Yes	130	~350	SAE #3 / Chevy (both)	2500	9
Cummins 6BT 12 Valve, Rotary Pump	5.9L	Yes	160	400	SAE #3 / Chevy (both)	2500	8
Cummins 6BT 24 Valve, Inline Pump	5.9L	Yes	305@2300	555@1400(!)	SAE #3 / Chevy (both)	2500	9
Isuzu 4BD1T from NPR Box Truck w/ Standard Trans	3.9L		121@3000	Approx 250-200	SAE #3	2500-3000	3-4?

Output Specs and Web Site Contect stolen Directly from website of
Mark's Adapters of Australia (New Window).
 

GM DIESEL ENGINES
ENGINE MODEL	CYL	DISP CC.	TYPE	POWER Kw@RPM	TORQUE Nm@RPM
OLDS 5.7	V8	5700	DIESEL	94@3000	305@1600
CHEVY 6.2	V8	6217	DIESEL	116@3500	386@2000
CHEVY 6.5	V8	6500	DIESEL	120@3400	394@1700
CHEVY 6.5	V8	6500	DIESEL TURBO	140@3400	515@1700

 

Look for more information about comparing these engines shorly with 
more accurate output statistics.

This has been stolen from Drexx Laggui as posted to the LCML

Duramax, V8 (6600cc / 6.6L / 402.73 ci)
        Max. output: 300 hp @ 3100rpm
        Max. torque: 520 lb. ft. @ 1800 rpm
        Weight: 833.8 lbs
Hino J08C-TR, I6 (8.0L / 486.0 ci)
        Max. output: 252 hp @ 2,500 rpm
        Max. torque: 550 lb. ft. at 1,500 rpm
Chevy, V8 (6500cc / 6.5L / 396.63 ci)
        Max. output: 187.6 hp @ 3400 rpm
        Max. torque: 515 Nm (290 lb.ft.?) @ 1700 rpm
Ford Powerstroke (Navistar T444)
        Max. output: 250 hp @ 2600 rpm
        Max. torque: 460 lb. ft. @ 1600 rpm
        Weight: 928.4 lb
Cummins ISB, I6 (5.88L / 359 ci)
        Max. output: 235 hp @ 2700 rpm
        Max. torque: 505 lb. ft. @ 1600 rpm
        Weight: 961.4 lb
Toyota 1HZ with Safari Turbo+Intercooler  (4.2L)
        Max. output: 263 hp @ 4000rpm
        Max. torque: 435Nm @ 2000rpm
        Weight:         650+ lbs.

Drexx Laggui  -  TLCA #11841; PMC
San Jose, CA, USA

The following is stolen directly from the Toyota Land Cruiser FAQ by Rob Mullen.  As the new FAQ becomes available this text will be removed and properly linked.  Any items inserted by andre@collegeinternetsolutions.com are colored red.

17.2 Diesel Engine Swaps 
- ------------------------ 
I'm starting here because to me this is the swap that makes the most sense for a rock-crawling machine and is probably the least explored. As you'll figure out shortly, I'm pretty opinionated on this one and I welcome anyone to dispute my views. I believe that diesel engines are superior to gas ones for offroad use for many reasons. They tend to make usable torque at much lower engine speed than gas engines. This means you don't need nearly as low a crawl gear. They also feature a much flatter torque curve. There is no ignition system to fail because of moisture. They are not as affected by altitude, in fact, turbocharged diesels are virtually immune to altitude. In most cases, even though they have all the advantages of a fuel injected engine, such as the ability to run at extreme angles, they rely on mechanical injection which is considerably simpler than electonic injection. Diesel engines also tend to get much better fuel economy and greater cruising range than gas engines of similar displacement. 

There are three commonly available engines that are suitable for swapping into Land Cruisers. 

The most easily obtained is the GM 6.2l diesel. It was offered in Chev/GMC Pickups, Suburbans, and full-size Tahoes. A conversion kit is available from Mark's Adapters in Australia to mate a GM diesel to a Land Cruiser 4 speed manual or automatic transmission. The GM V8 weighs about as much as a big block, so pretty close to the weight of a 2F. 

The GM 5.7l is without a doubt the worst diesel engine ever cobbled together. It is the Olds 350 block that was converted to diesel. Probably 99% of these motors have been blown apart for at least 10 years, but some may still be kicking around. If someone offers you one, they are NOT your friend. 

A slightly more rare engine that I see as being a better match to a Land Cruiser is a Cummins 4BT3.9 litre turbo diesel. It was used in among other things, Ford E350 cube vans, Chev/GMC P30/P3500 step vans, and Case 580 Tractors. 

PowerMark used to offer a conversion kit (p/n RK9525G) that will allow you to bolt in a B3.5/5.9 in place of a GM 292 I6 or 350 V8. In order to put this engine into a LC using the stock transmission, you simply need to get the motor mounts/bellhousing Advance Adapters sells for putting a V8 in and use the Cummins engine instead. Unfortunately, it appears they've recently gone out  of business. Stay tuned... Thankfully not, AA is still very much so in business.

I think the Cummins B5.9, as used in Dodge Ram is definitely too heavy to put into a 40 series, and is a little heavy for a 55/60/80 series. The above mentioned kit would also work for a B5.9. 

The best diesel swap into an FJ40 I've ever seen is the Isuzu 3.9L diesel. Two of its applications were in Isuzu NPR series cab-forward trucks, and BELT LS2700CII (4BDIT). 

17.2.1 Isuzu Engine Specs 
- ------------------------- 
DISP (INDUST) TORQUE COMP 
MODEL (CC) CYL FUEL BHP* FT-LB RATIO 
4BD1 3856 4 DD 88@2800 181@1600 17.1 
4BD1T 3856 4 TDD 105@2500 240@1600 17.5:1 

*Figures according to SAE J1349 Gross BHP test. "Automotive" BHP of the 4BD1T for instance is actually 121@3000 

17.2.2 Cummins Engine Specs 
- --------------------------- 
DISP TORQUE DRY WT LENGTH HEIGHT 
MODEL (CC) CYL FUEL BHP FT-LB (LBS) (IN) (IN) 
4BT3.9 39xx 4 TID 105@2500 260@1500 705 30.1 35.6 
4BTA3.9-120 39xx 4 TIDA 120@2500 302@1500 725 30.1 35.6 

17.2.3 Diesel GM Specs 
- ---------------------- 
YEARS DISP STOCK TORQUE COMP 
MODEL AVAIL (CC) CYL FUEL HP FT-LB RATIO 
5.7L 57xx V8 ID ..... ...... ...... 
6.2L -94 62xx V8 ID 150 250@2500 ...... 
6.5L 94- 65xx V8 ID 170 290@2000 ...... 
6.5LT 94- 65xx V8 TID 190 385@1700 ...... 

17.2.4 Nissan Diesel Specs 
- -------------------------- 
DISP TORQUE COMP 
MODEL (CC) CYL FUEL BHP FT-LB RATIO 
SD33T 3245 6 T?D 101@3100 175@2200 21:1 

MODEL BORE STROKE DRY WT LENGTH WIDTH HEIGHT 
(IN) (IN) (LBS) (IN) (IN) (IN) 
SD33T 3.27 3.94 

FUEL 
ID - Indirect Injection Diesel 
DD - Direct Injection Diesel 
T - Turbo 
A - Aftercooled (erroniously called Intercooled by most)