Sorry man but that's about a shadiest sticker I've ever seen. I'm actually a specialist at this stuff, being a 4x4 importer myself, off and on since the 90's and heavily experienced with Ca. DMV/CARB issues. RHD/LHD has nothing to do with it, it's the grey market diesel engine which is 100% not smog legal unless it was CARB certified with great expense (averaging $10K, and only for certain motors). Did you not ever notice how few grey imports are sold in Ca.? This magic van-man you are talking about.. who is it? What dealership? How does he get around laws that 100's of others can't? These vans are canceled by Ca. quite often actually. You joined this site to make a quick buck which happens all the time, but I like to warn people who may not realize the issues they could face based on my background doing this for so long... nothing personal, its just the way CA. is.
Grey market diesels are only smog legal if they are pre-1980 in Ca. with pretty much no exception. This van may have fallen through some loophole that someone overlooked before they cracked down on all this stuff years ago. You might get lucky with the sale and the next owner might get lucky as well. Hopefully they won't get a busy-body at CARB or DMV because if so, this will be 49 state legal only at that point. Just ask any of the 100's of guys who try this kind of thing in Ca... from imported Rovers to Cruisers to Gwagens and on and on... many cases of canceled registrations, nasty letters from CARB after getting tags, sometimes a few years after getting tags! ...and so on.
And by the way, a dealer can not "certify" any engine in any way. Someone told you a bunch of BS on that point, unless maybe they did that a very long time ago but without a current CARB/Lab sticker or original Ca. EPA compliance tag, it's not CARB legal, period. Dealers have ZERO ability to deal with grey market certification. People go through hell with these issues and many have lost their butts in fees and/or having to sell their investments due to shady sellers or sometimes just ignorant sellers. Do some research before promoting something with all that false confidence and listen up. Lay low and hope for the best is my advice (and people have paid me for importing advice).
Good luck!