Determining original VS. repro Wide Tread GT's

[tom406]

A friend of mine asked about ID'ing original F70-15 Wide Tread GT's versus repros. I know a lot of the visual cues on Polyglas tires(Made in Argentina vs. USA, the textured band near the wheel opening lip, etc.), but was stumped by this one. Any help out there? Also, can anyone read the date codes on the tires (to determine if his Wide Tread GT's are '69 vintage, or '71 vintage, or newer?) Thanks for the help.

(On a slightly related note, since some Z28's have been documented with Firestone Sports Car 200 tires, I was wondering if any of the Yenko/double COPO cars with 15" Rallys might have been so equipped. Or did Goodyear hold the contracts when most of these cars were produced?)