Can anyone elaborate on the pro's and cons of replacing an engine from a 500SEC (m117.963) with one from a 560SEC (m117.968). Are there any special conversions or problems to anticipate? I know that the gear ratio is different, so should this become a major concern, or is there anything else I should be looking at? I was told that an engine from a 560 would fit right into a car that was originally fitted with a 500 with no problems. This would be desireable, since I've found a great deal on an engine from a 560SEC, and the one in my car now (500SEC) has to be replaced or will require a major rebuild.