Firestone tires

[Mr70]

That is possible Tom.
That particular Firestone plants history record is spotty at best.It first looks like it was not making tires within that year,but upon further review,sporatic reports show production as early as mid 1970.The letter L at the end of your first tires code may be an indicator for an early produced tire,but I can't confirm that.
There is no determined beginning date shown at this plant,as those files are missing.
A plants records are a helpful indicatior of when a tire was originally made.
Yours is one that didn't keep very good records.