Which one? According to
duckduckgo.com/?q=Panhard+CD+Peugeot+66C&ia=images The 1964 and 1967 Lemans entries have distinct differences.
Rather than changing the body into something else, I could see sacrificing lateral acceleration and go to tall narrow wheels and tires with as much negative offset as possible to accommodate four wheel skirts.
Freevalve four-cylinder?