Is SEER the only information your looking for on that old girl?
Most likely correct.A 1978 unit may not have a seer rating.
It may have an EER rating which is derived from testing at 95F outdoor/80F indoor.
Probably in the 6 to 7.5 range unless it was something fancy.
Just remember- don't assume what you have now is the correct size.
My thoughts, too. Just morbid curiosity or something else?Why are you inquiring? Are you replacing this unit?