It would be interesting to see documentation for the machined 15X8's on a 1978 car. I tend to think Joe Bays has this one correct. However, he does leave open the possibility of machined 15X8's on a 1978, he just hasn't seen any documentation that they were included in the 78 model year.
Joe also makes the assertion that the Y88 had nothing to do with the all gold wheels since a Y88 could come with the 15X7's (which had machined edges) on the non WS6 models.
My old 78 came with rally wheels. A friend of mine gave me two all gold 15X8's. This was around 1980, well before ebay. I had a heck of a time finding two more. I remember calling Western Wheels (the manufacturer) to see if I could buy them direct. They told me no, that they had a exclusive with GM. Does anyone know if all the snowflake wheels were manufactured by Western Wheels?