From 1958 on, the first Shanghai cars were all some kind of soap green color. Many things in China were painted in this color -even in the early 1980s- (like other consumergoods, hotel rooms etc.)
This car is a strange looking replica (I am about 95% certain) of the Fenghuang, the predecessor of the Shanghai SH 760. This replica is built on a Wolga M21 as basis.
It is possible that the car is a unique prototype. But I doubt it.
SAIC has another replica of the same car, in their headquarters in Shanghai.
All these cars are described in my document: "Shanghai, saloons from the artisan era." (see http://www.chinesecars.net/index.php?page=4).
Hello Joest Jonathan,
Never seen this thing. I agree with your second idea: a modern chassis and a home made old timer. There were more of these vehicles, sometimes at auctions, but also since the 1980s in the film industry. (In a country were all cars were destructed at 15 year of age there is not much antique left...)
About the soap green Shanghai replica; underneath the television tower (Oriental Pearl Tower) in Pudong there is an interesting museum describing the history of Shanghai. There in the cellars are some car replica's (you don't understand why they make these replica's as restoring some old would have been easier and cheaper...). there are one 1910-1920 replica, two 1930s replicas, and an original postwar Buick Eight and Willys Jeep.