I bought a brand new pair of Eagle STs more recently than that...but not much! It was somewhere in the 2004-early 2006 range. I loved how those tires drove.
Just checked my spare in 70 mustang. Been in trunk since 87 when i bought it. Thank goodness never needed it. Shellride 7.35-14 Dont see any datecode. Does say made on USA.
No steel belts, probably be fine. Likely has nylon or maybe rayon cords. The '71 Comet GT parts car I bought a few years back still had it's day one, Firestone Deluxe Champion 6.45-14
They're only required to put the date code on one sidewall, right after "DOT". Tires made before 2ooo might only have one digit for the year since it was assumed they wouldn't last more than 10 years.