[Special Coupe Frank]

There are three standard sizes of six-volt battery today:

Group 1 ( smallest, fits Model T, Model A, Chevys with the battery under the floor...)

Group 2 ( will NOT fit the tray in a T/A Ford, Chevy; used on 1935-'55 MoPar, etc)

Group 3 ( Heavy truck, usually wired in series for 12-volt or 24-volt operation )

Then there's the "long skinny battery", as used by Buick, Packard, Caddy in the '40s & early '50s...

Group 1 is what you need. If it's a little short, a plywood spacer will take care of that.