The missing parts are the hook assembly (hook and bobbin case base) and the bobbin case. The bobbin case base is the part with the finger that is in the middle of the hook assembly. If buying used parts make sure that the parts are from a 221 and not a 301. The finger on the bobbin case base is slightly different between the 221 and 301. They are not interchangeable. The 221 style will fit the 301, but not stay in between the springs of the throat plate when running at normal speeds.
I have had nothing but trouble with the Chinese made bobbin cases that I get from my wholesale house. Everyone has had to be adjusted by grinding and sometimes replacing the flat tension spring. Buy a good used bobbin case if possible.
Cathy