The group 56 battery fits the original battery hold down and tray in my 55 Ford car and had a hard time finding one locally,none of the usual places even had a spot for one now where 10 years ago when I bought the previous battery I had no problem. Rural King had only one so I am kind of curious on what that battery was designed for as it might help me find another or will just have to get a generic battery tray and hold down the next time it needs a battery.
I changed my '55 over to 12V and a common 24F battery fits the battery tray using an aftermarket replacement holddown. Tractor Supply carries the correct 6V battery for '55 Fords.
Wally world,one local Autozone and TSC did not even have a place for one,this one fits the tray and hold down and is around 580 CCA and 700 CA and started the 351 for two months short of 10 years. I took the last one RK had.
Ford used them a lot in the 80's as Squirrel said. It was much lighter than previous batteries so they used it all but larger cars and trucks. Save weight, increase milage.
I converted both my Ford 8N and 850 tractors to 12V a while back, and researched dimensions to fit, and a 35 battery was very close to the original 6V, fits right in there, in stock at both the old truck, tractor and auto parts store in town, and Tractor Supply
I have at least 5 years before I have to worry about getting another,its kind of a small battery but it did its job for almost 10 years.