That is the fusebox door or the oddments tray. There are two versions. The 1974 definitely got the new door but I have seen some '73's with it also. The early door had a push button, and the late door has a knob that you rotate. The button and knob aren't interchangeable, but you can modify a late model door to receive an early button (but not the opposite). Your door won't close because you have no button. Also, the actual striker on the button tends to wear down, making it difficult to close even if you do have a button.
Yours is nice enough to be restored and re-flocked. You will also need the bracket that holds the prop/spring that limits travel. You are also missing the hinge, which may still be visible under your bank of fuses. your button is also missing. Good approach to get a new one, but don't toss the old one. List it for sale.
I paid $150 for mine several years ago, and it it was in very nice condition.