Hi Nedim,
Tape heads do not have a standard unit assigned to them like capacitors, inductors, or resistors have. Tape heads are all slightly different, mechanically and magnetically. Hitachi part number 5444581 is really only going to be useful if you are looking through service manuals for similar Hitachi models that might have a chance at having that same part number for the tape head. Then you have to find someone selling that model, and buy it just for the tape head.
You can try different tape heads from other Hitachi models, or other manufacturers, but they may not sit in the proper position in the deck or give a good quality playback signal.