I am restoring A Heath Kit SB200 Linear Amp.
According to this link, if the value on the part is underlined, then it is rated for 100V.  If there is no underline, then it is rated for 500V.  If they are marked 1kV, then they are rated for 1000V.

After a quick look around the handbook for the SB200 (which you helpfully didn't provide,) I'd be inclined to use parts rated for 1000V.  There is an 800VAC section that generates DC.  At least a couple of those ceramic caps are in places where the chicken in me says "I'm not gonna chance it." Many others are in places where a lower rating would be OK, like on the filament power.

You could use 2 capacitors in parallel to get 0.02 microfarads.  Use 0.01 microfarad capacitors and use two in parallel for each 0.02 microfarad part you replace.



You shouldn't really need to replace a ceramic capacitor unless it is broken.  They aren't like electrolytics or paper and oil, which can dry out and go bad.