That is a 6BB1, which is basically a 4BB1 with 2 extra cylinders (same goes for a 6BD1)
EDIT - btw - that looks like a Series 3, not a defender. If the adaptor is designed to fit in place of a 200tdi, then it will bolt to an LT77(S). With one or two very minor mods it will bolt to a series box, and wth a couple more mods it should bolt to an R380 or ZF auto.
Not sure if I would trust any of those boxes behind it though! Torque pulses wuld be smoother than a 4BX1, but peak torqu would be huge, and from very low rpm.

