The 6BB1 is a very nice smooth engine. But it's far too big to fit without major work. Approx 5.4 litres.
The 4JB1T is nice, but you'll be able to pickup and bolt in several 300tdi's for the same money. The 300tdi will produce similar power and torque as the SD33T, but the direct injection of the 300tdi has stronger pistons, stronger head and far better efficiency.
4BD1T's are the best engine you can easily fit. But they aren't cheap or plentiful. They will also turn most landrover gearboxes inside out. Capable of over 200hp and 700Nm with the stock injection pump.

