if it's a euro 500sel, then mileage will be an issue and any swap will be expensive. the euros are not tuned for emissions and tend to be thirsty.

the u.s. got a 500sel in 84-85. 10 years ago, had 1 that a customer bought for commuting around orlando. sold it after 6 months because the mileage was approx 16 mpg/hgwy. not a good daily driver today.

it needs to be inspected for timing chain wear and other issues any 40 yo car would have.