Even though they share Many parts the SEL is 4 inchs longer (rear leg room) than the SD,they are quite different cars to say the least.If you have been driving a deisel you have to learn a whole new bag of tricks to maintain and repair a MB V8 if you don't do your own repairs and both cars are in similar condition my guess is that it costs about half again as much to keep the V8 on the road.
Now the real hard part.If I had to choose between between selling my 81 SD or my 86 Euro 500 SE (has Euro 420 engine)I'm afraid the cost of weekly visits to a head doctor that specialiizes in dual personalities would far out weigh the selling price.
OHHHHHH that smooth power and the sound of that V8 as it climbs near redline while passing that Lexus. "I can't belive it took me so long to figure out that the best car on the road is an MB deisel" So watch half a dozen con man movies and then persuade your wife how buying both will bring you wealth and happiness...........
William (Con Man) Rogers.....