I have a 1954 auto with 6 volt ignition and it has many radio capacitors in the car that need replacement, none have any voltages visible on the cap, does anyone have any idea what values would be good replacements for these?

The primary ignition voltage can spike to 300 volts when the contact points open and the ignition coil field collapses. You may want a ~500 volt capacitor for this distributor application. I believe that the common value is .047 uF (.05 uF).
Generator and radio filter capacitors can be ~50 volt rating.

The typical failure mode for ignition caps (which were always called "condensers") is leakage. An ignition cap should last quite a bit longer than a set of points.

When used in the ignition circuit, the primary purpose of the condenser is to aid in stopping current flow immediately, so as to not burn the points, and so as to create the largest voltage spike in the secondary as is possible. It is critical that this capacitor be of the correct value and that it have no leakage. Leakage will cause a reduced spark, and incorrect value will cause the points to pit. There is actually an article written by Delco Remy regarding capacitance adjustment to compensate for point pitting, depending on the direction the pitting is taking place.

Most other radio capacitors on the 6 volt line should not cause concern unless their leakage gets quite low in resistance. Replacements can be obtained from your local automotive parts store.

T.