If it has engraved letters like "J1" (which is their laser copy of a Yamaha "CY" headjoint), then you are good to go. Those are excellent headjoints!
If there is no engraving at all, then the flute is desirable only for the body and foot joint. A new modern headjoint will have to be purchased.
Additionally, if you can find out if it was built to the older Gemeinhardt scale or the newer Cooper scale (introduced into Powell Flutes in 1975), that would also be extremely helpful.