You can also try to get in touch with some members of the Buick Club and try to get some length measurements of the body but must be the same body style. I agree with Sean on the wheelbase measurement but it might be difficult on the 60 and 80 series, since there is only 3" difference. Whatever in turns out to be, it is a rare body style. If a 90 series 556 were made, if a 80 series 758 were made, if a 60 series 2887 were made and if a 50 series 4118 were produced. The figures are for USA production. There were some exported in each series but not many.