I am the one time owner of 66 gt350h sfm 6s1852 sold to someone in Northern suburb of Chicago Illinois around 1975 or 1976, then off to Wisconsin I believe. I have many pieces of original information for current owner as I owned the car for several years.
SAAC keeps records of owners if cars have been registered . Your best bet should be to contact Howard Pardee the 65/66 registrar. You can got to the website get his email there. Bob