I'm really sorry to hear that. It does suck....
I agree though. If the whole car is still in great condition, try the 4.2L engine or better yet find a 5.6L. Make that 560SE
or take the badge off and let people think it's a 300SD.
I'm not sure how different the tranny and rear end are, so let's wait for the techs!
The brakes on the 420 and 560 are bigger too I think (at least the fronts)
I'm also almost positive that the exhaust would be different.