[Mondial]

I am using 400V caps because that is what happen to have. I would prefer 630V ones, but they are a bit more difficult to find in 1 uF ( I am using two in parallel for the 2 uF cap ). Actually, in circuit they will be only about 200 to 250V max across them in normal use.

During warm-up when the rectifier filament is hot but the remaining tubes heaters are still warming up, there will be momentarily higher voltages across some of the caps, but not significantly more than 400V.
Cap 28 ( rated 450V ) sees the most voltage because before the 6A7 warms up, the cap is connected directly to the B+ supply through 20K resistor 26 without any voltage drop from tube current. The remaining caps see less voltage because of voltage divider resistors.