That is the common misperception. The Polyglas was a 1970 model year tire. Everybody puts those on their cars because they don't realize that the other, more correct tires are available from Kelsey Tire.
I believe the Goodyear Speedway Widetread was the available Goodyear tire for 1969. There were other makes of tires used as well. Here is a photo of my old Z11 from 1970 with its original Speedway Widetreads on it:
Here's the info from the Kelsey Tire website:
http://www.kelseytire.com/pages/preformancetires.html
"E70/15 – Speedway Wide Tread RWL
Specifically designed and only fitted to the 1968 and 1969 Z28 Camaro. Goodyear answered the call from GM to develop the appropriate tire for this high performance platform. Talk about a Z-handler, this Goodyear Speedway Wide Tread GT did the job. "