Just measured mine - as far as I know they should be the original ones on the car my Dad bought new.
Both are 13 inches (and a bit dried out but still fine).
The parts book (I never can follow it) shows it should be p/n 8349 but the only Tbird listing (S) is for a 64. Funny - some other Ford car radiator seals are listed as "R.H. - tire carcass"
(you can just see the top edge of the one on the drivers side in this old pic from when I was adding A/C)