I used a 4JB1-T sourced from a used parts dealer out of Japan and a mating kit from GB.
I had heard rumors of someone from New England putting a 3.9L Isuzu diesel (probably a 4bd1t/2t) into a RR but he did a lot of custom fabrication to get it in there. The 4bd1t/2ts don't generate more HP or torque than a 4.6 RR V8, but I have heard that the 2.8 International PowerStrokes required modifications to the drivetrain to work in a RRC.
I've already put over 20k on my 2.8 and love it... driven it from ME to CO a few times now and no major issues with the engine...
'94 RRC County TDi (2.8 Isuzu 4JB1-T)