c1flyout-
I seem to recall reading all FE motors (352,360,332,390etc) were stamped with that 352 and it had nothing to do with the displacement although I don't recall the reason for that particular number being on the FE blocks.
My Ford reference books show nothing smaller than a 390 being offered in the T Bird in 1963. The T Bird engines all carried a name like Thunderbird V8,Thunderbird Special,Thunderbird High Performance or something to that effect.
My guess would be it probably is a 390.
Good luck with your "new" car.
Mike
I'd rather be lucky than good.................
but good ain't bad!!