Then you guys are really going to hate my 1967 Mercedes W110 station wagon when I'm through with it. It's an extremely rare vehicle, but I sold the original 6 cylinder gasoline engine and installed a 5 cylinder turbocharged diesel engine. I'm also going to transplant what's left of the body onto a long-nose W111 sedan to make it into a W111 station wagon, and will add a sunroof. They never made my dream car at the factory, so I am going to build it myself and enjoy it for the rest of my life as a daily driver.
The thing is, it will look stock, not customized, even though it has been customized. It will look the way the factory would have done things. It will have more horsepower than the original engine, more torque, and much better fuel economy while being easier to work on--and will last longer between rebuilds, as well as the ability to run on biodiesel.
I do agree that hodge-podging a car together and doing a hack job of it to get a few more miles out of it until it conks out for good is a big disservice. I've seen a lot of cars where parts were made to fit to get the driver by for a few more miles, and then junked the car once something major broke.
I have seen the occasional Chevrolet 350 V-8 in 450SELs and thought, "What?..." But, then again, from a practical standpoint, once a 450 engine wears out, it may be more cost-effective to install a common engine that is more easily serviced at your local garage. I dunno...