Past link on a six volt Pertronix installation but it pertains specifically to the Load-O-Matic distributors.
http://www.y-blocksforever.com/forums/Topic6983-5-1.aspx
And the link to the Pertronix website catalog showing the ignition conversion kits.
Pertronix catalogues
For the L-O-M distributors and per the catalogue, the conversions are available in both 6 volt positive and negative ground. No footnotes for the ’57 and up dizzys regarding six volts though. It would be worthwhile contacting Pertronix and seeing if this is something that’s easily available on their end. And they would need to know if the vehicle is positive or negative ground as that will make a difference.
Another possibility is to redrill the ’57 breaker plate for the L-O-M six volt module if the rest of the conversion kit is compatible.

Lorena, Texas (South of Waco)