where o where to find a correct size 40-53 battery

[Wheels of the Past]

So I am trying to find a correct size 2HF 6v battery for my 46 Pickup. One that fills the battery box as well as the hold down. All I can find is those $400 Ford script jobs for show cars. Does anyone know where to buy a good old 10.5 x 7 inch battery without spending so much for a original 35,000 mile vehicle we plan to drive every day??