There are alot of 300CD's turbo and non-turbo running around. It would be less hassle and cheaper to find a stock one and enjoy it.

http://cgi.ebay.com/ebaymotors/1978-Mercedes-300CD-diesel-couple-in-great-condition_W0QQitemZ4638087879QQcategoryZ6330QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://cgi.ebay.com/ebaymotors/1981-Mercedes-Benz-300CD-Diesel-Coupe-RARE_W0QQitemZ4637203940QQcategoryZ6330QQssPageNameZWDVWQQrdZ1QQcmdZViewItem