Goodyear tires from 1966-69 had seven (7) characters in the tire code...a mixture of letters and digits. In 1970-71 they became eight (8) characters...all letters. The tires from 1966-1971 had VYTACORD POLYESTER CORD embossed on the sidewall.
Reproduction tires had a twelve (12) character tire code beginning with CYUY (see pic below). The sidewall reads POLYESTER CORD.
NOTE: The tire pictured below has a tire code ending in '704'; which is the month, '7' (July) and year '04' (2004) of production.
The lone difference on the tire code in my sample versus the one being sold in this thread is the date of production.