You can't fool me! The REAL question here is "What do you think about replacing the motor in a Mercedes-Benz with a Ford V8 (or V10!)"??????
As I recall this was done a lot in the '80's, usually a 302 into a 280S, etc. Had a friend who had one: it actually ran damn well, didn't overheat, got good mileage, etc. He said he got the car (with a blown engine) for under a Grand, had the motor (a fresh rebuild) sitting around, and spent more on the install than what he had in the two together. He just loved it and drove it to work (about a 50 mile round trip) for over 5 years. Never a problem. Thought it was a sharp idea as it worked out great for him!
There are pretty good programs available for putting the 302 or a 4.6L into the 7XX series Volvo, a 350 in older Land Cruisers, V8's into Miata, the previously-mentioned 350 into Jaguars...
Ever hear the term "Hot Rod"? How's about "Chopper"?
I know if I had access to a clean, older RR with a blown motor, for the right, RIDICULOUSLY LOW pri$e, I might take a look at a rebuilt 454 and a Turbohydro, or a 440 and a Torqueflite, or a 460 and a C6: you could probably sell the RR transmission and pay for the entire swap!
For some people it is all (and ONLY!) about their own self-image. Look at the house, the toys, the Trophy Wife! Other people seem to be less concerned about appearances and more concerned about actually living. IMHO, of course!