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Cummins 4BT in a FJ55 dialect
Size and dimensions for the 4BT are available here
Conversation of getting a 4BT to fit into a Cruiser

What originally spawned me into the idea of doing a Cummins swap into a Land Cruiser was the idea of putting a Cummins 6BT into a Toyota Land Cruiser.  I had seen these pictures which got me excited.  The biggest factor that appealed to me was the idea of massive amounts of power in the Land Cruiser, but with the economy and ruggedness of a diesel engine. 

However, not knowing anything about Cummins engines and the 6BT at the time, I have now decided in most applications the Cummins 6BT is too large, heavy, and usually too powerful for a Toyota Land Cruiser in my opinion unless significant modifications are made.  However, I have now also seen a FJ40 with a 6BT in it (and it actually fit).  I have now changed my mind about some 6BT swaps into Cruisers, I think they are actually an awesome power plant in some Cruisers.

For me, the next best Cummins option in my opinion was the Cummins 6AT, which, after I've seen it retrofitted into a FJ55, I believe will easily fit into a 60 or 80 series Land Cruiser.   I also think the 6AT is an awesome swap for a Cruiser after seeing one done and doing the research.  However, desiring more power than the 6AT can offer as stock levels (and not having heard a whole lot of information about 6AT modifications), I looked into the next best option which came highly recommended by the Binder Bulleting International Scout enthusiasts which is a great group of enthusiasts who are highly knowledgeable... 

    ---to install a Cummins 4BT into a Land Cruiser.

• Size and dimensions for the 4BT are available here.
• The 4BT is very loud and rattly so it would not be a good candidate for a FJ40 or poorly insulated FJ55.  However, Lou Chou writes: Vibration is not too bad.  My 4BTA running is pretty smooth, but not as smooth as the 6 cylinder B version. Start up, idle and driving is very good. But when shut down, the engine shakes a little bit. When run in 5th gear, it is smooth and quiet. Around town is pretty noisy. I might plan to put some sound proof lining on the firewall later. 
• It also has relatively poor acceleration.
• The 4BT is basically a 6BT with two cyl removed.  It sits shorter so it should make room for an intercooler and larger radiator that will most likely be needed.  Many of the same performance parts for Cummins 6BTs also work for 4BTs.
• The same factors that apply for the 6BT regarding suspension lift apply to the 4BT because they are the same height.  Therefore, you can only run this motor in a Land Cruiser with at least 4" (I plan on 5-6") of lift.
• The only Land Cruiser I'm aware of that has the 4BT installed in a Land Cruiser that I am aware of is this FJ55 built for rock crawling.
• It has the same bell housing and bolt pattern as a 6BT.  You can use a NV4500 or auto tranny for a V8 but I personally still do not think it will be as beefy as the NV4500HD that comes behind 6BTs in Dodge Ram pickups.  This is the only transmission with a decent reputation for being able to hold up the 6BT's torque, so I'm sure it will be more than adequate behind a 4BT.
• Because of the 4BT / 6BT's relatively low peak RPMSs (around 2500), you will need a 5th gear unless you are running fast axles and larger tires.
• You can use also use an adapter to mate the NV4500 to a stock split t-case from a '79 or later FJ40 or FJ60 to retain the use of the stock axles.  Advance Adapters also makes a cross member for the NV4500 designed to bolt to the FJ60 chassis. See more about this in the Cummins conversions transmission section and the Cummins conversions t-case section.