[SmallHurst]

The Z/28 only had the E70-15 Wide Tread GT and the Firestone Sportscar

I believe that we have discussed this on a separate topics.

The F70-14 Polyglas in RWL was being produced in 68 and was first introduced on the 68 1/2 Cobra Jet Mustang.
We know that the '69 Chevelle wore Wide Treads.
There were no memos showing a cutoff date when the widetreads were not being used and when the Polyglas were being shipped to production lines.
No Widetreads were used in 1970.
Production lines go through model changeover typically the 2-4th week of August.

We only know what we know......