Try Optima, I have gotten some 6 volt gel battery's from them, not sure about the size though. http://www.optimabatteries.com/publish/optima/americas0/en/config/splash.html
If it doesn't need to look original, try a Optima 6V Red Top Battery. If you still have the original battery, you could saw the top off, recycle the guts, clean it out and maybe fit one, or even two in series inside of your case and then silicone the top back on. Doesn't sound like much fun, does it? Maybe not. I found this at: http://www.diversifiedbattery.com/Optima_Batteries.html Optima Red Top 6V - 800/6 Voltage: 6 V CA: 980 AH CCA: 800 AH RC: 110 Terminal: Top - SAE Auto Pos Color: Red Top Weight: 19 Lbs Length: 10 Width: 3.5 Height: 7.8 Optima 6V Red Top Battery $125.00
Looks don't matter as it is hidden, the main problem is that it will need to turn of 460 cubes of inline 6, through very old style electrical not a modern high rpm style starter, if that is going to make a difference. Thanks!
OK, now I hafta know what kind of car (truck, tank, locomotive) that is, 460 cubes of inline 6 sounds interesting.......Pic? The Optima does have high cranking amps: CA: 980 AH CCA: 800 AH RC: 110
http://www.diversifiedbattery.com/Optima_Batteries.html Optima Red Top 6V - 800/6 Voltage: 6 V CA: 980 AH CCA: 800 AH RC: 110 Terminal: Top - SAE Auto Pos Color: Red Top Weight: 19 Lbs Width: 3.5 Height: 7.8 Length: 10 A PAIR of these in parallel would fill the bill.
Sounds like something that may have been in an over-the-road truck in the 40-50s before diesels took over the truck trade, or some military engine from WWII or Korea befor ethe miltary became a diesel-carried operation.
Someone told me to get an 8 volt battery for starting larger engines or using in colder temps. I assume you can get those at tractor supply stores. Apparently they are safe for 6v systems but give you a little extra oomph for starting which I may need as I plan to drive my 54 Chevy on cold days if the roads are clear. Anyone here use an 8 volt battery? Todd
My high school teacher ran one in his '35 Ford years ago. It started better but it was a little hard on the 6 volt lamps. He said the regulator had to be adjusted to give enough output to recharge the battery. I have seen batteries with 3 posts on them, ground, 6 volt positive and 12 volt positive. You might consider putting a 12 volt generating system on the car and power the 6 volt stuff off the lower voltage post. I saw this done in a '48 Ford a year or so back.