Anything 1000V or higher ought to work...If you didn't buy anything like that and need to order it may as well grab a 1200 or 1600V part for headroom.
The 0.05 and ~0.033uF 1000V damper caps are one of those parts that after doing a few 630 based sets (and others that use FLY1 like some Admirals and DuMonts) you can practically look at the set in it's cabinet and start the parts list with those odd duck parts.
