The first series 1955 models were 6 volt, the second series were the first of the 12 volt Chevrolet trucks. A 1955 1st series is not a particularly common model, so I would keep it original if it were mine. There is nothing wrong with 6 volt systems, but you have to keep the battery terminals and cables clean. But you have to do that with 12 volt systems, too. I don't know the production numbers for '55 1st Series trucks, but I'm sure someone here can provide the number.
The switch to 12v systems was primarily driven by increasing electical loads. With 12v systems, you can use smaller wires and lower current for the same power requirement. Smaller wire means smaller and maybe cheaper wire harnesses. That idea was the motivation for moving to 42 volt automotive electical systems a few years ago, but that movement fell apart (or lost power, if you like) a couple of years ago.
There has been a lot of information posted here on 6v-12v conversions. Do a search on the topic, and you will find enough reading to keep you busy for quite a while. But I would keep the truck original if it were mine.
Harvester
