This 57 W500 was on E-bay a while back, it sold for $1,825.69

http://cgi.ebay.com/ebaymotors/aw-cgi/ebayISAPI.dll?ViewItem&item=598174309&r=0&t=0

It is a flat head six model with a VIN of 81010440 and the engine number T306*I2340I*

It sold to Ron L. of TX