I'm think it is a GM car, because of the windscreen and A-pillars which are of a similar style to those used in 1961 full-size models. Other styling elements also suggest GM. The shape of front fenders is similar to 1961 Buick (front) and 1961 Oldsmobile (rear), and the front bumper has these small fins which remind the downward-facing tailfins of '61 Olds and '61-'62 Caddy. So if it is not a Buick, then maybe it's an Oldsmobile styling exercise circa 1959-60?