The 8 volt battery has always been a band aid fix for a 6 volt system with problems. They are just like to old batteries we had 50 years ago that just didn't last very long. They were always more expensive than 6 bolt and since there is so little demand for them, I would assume them to be very expensive.
I have 3 old jalopies that have 6 volt systems with 6 volt Optima batteriess. I don't try to hide them because things like a 302 in a 46 GMC isn't original looking anyway. I have 4-0 cables which I keep in stock for my trucks and they work fine. However, if I were to use these jalopies on a regular basis, I would convert them to to 12 volt because there is no question that 12 volt is better because it requires half the amperage. Back when we used pre 56 GMC trucks in our business, we converted to 12 volt by having one group one in the battery box and another group one on the firewall in series. That cut our electrical problems by a lot and then when we added one wire Motorola alternators, we figured we were on the cutting edge of technologies.
I keep the 3 jalopies I have on 6 volts simply to prove that it can work if it is properly maintained and cables are heavy enough. But I would never try to argue that 6 volt is better. I knew that back in 1957 when I drove a 1950 GMC to school and parked it on a side of a hill to make sure it would start.
