I have both a 230 SL (1964) and a w123 230E (1984) and although the w123 2.3 inline four is a great little engine that is almost as smooth as a straight-six, I wouldn't consider going in that direction unless it was absolutely necessary. But I know that there are still a lot of w123's in Egypt and the Middle East, so sourcing parts probably would be a million times easier and a lot less expensive...