Hi David,
It all depends on what you want the radio for.
A radio with torn grill cloth and a missing knob may not be good furnature for your home. If it hangs around a while like that you may soon get sick of it.
If you have a safe place, you may want to keep it there untouched. I think in about ten years untouched radios like this will be quite rare.
However, if you want the challenge of getting this working, you are with us!
Grill cloth is now only available as reproductions as far as I know. I do know that one place did specialize in grill cloths. I don't have the web site anymore since I have a drapery place near by.
Knobs for this radio do crop up on eBay rather frequently, so you may be able to win an original there.
Other parts for this radio are readily available.
I do have some reason to believe that the schematic for this radio on this web site may be wrong. Usually the 'B' in a Zenith model number from this vintage is a battery operated radio.
It looks like this radio is a console set. It has three bands, two of them short wave. It has an RF amplifier stage which will make it quite sensitive, too.
Cleaned up and working, it will look and sound wornderful.
Best Regards,
Bill