Post a photo, because I doubt you have an FN T series, but an Inglis with a T prefix. Supposedly the "T" was for Toronto. This Inglis should be the fixed sight No2.
FN Hi Powers started with the letter T as in "T123456", but the Inglis HP's had a number before the letter "T" as in "0T1234" up to 9T3628 which is the highest I've read about.
Inglis etched the serial#'s after the pistols were Parkerized, so an original Inglis serial# will be "in the white".
As far as value? If its a mixmaster parts gun FN T series frame with an Inglis slide........less than a complete Inglis or a complete FN.