I know the 55 Ranchero I have on the hill that you looked at has a VIN and it has four additional digits on the plate that are not supposed to be there. The last digit is a p. Ford confirmed that there was 6 prototype Rancheros made in the Dallas plant and that is where mine came from but I have never been able to confirm that it is one of the 6. It was a production vehicle overseas in 55.