Hello Rightnow,
As far as I know, there are no plans of equipping the R-Class with the '420 CDI V8 diesel engine. Sales in Europe have been poor and there is no need to add an engine to an R-Class model which will sell in even poorer numbers.
The R320 CDI 4Matic should be powerful enough. I've driven it and it's not slouch. Here's the review:
Link:
http://www.caranddriver.com/idealbb/...earchs tring=
