My race stuff is at work at my race shop.
So I just now took a spare container home to see if it would fit my mopar pig.
My pigs weren't really on the floor, a bunch of other stuff was. lol.

It fit's but it's a little smaller than a 9". It could be made to work with a thin sheet of sheet metal as a adaptor plate. Or it even could be bolted down without one.

I have been through a few rear ends in my time and have 4 of these containers, sorry none are for sale. jAZ USED TO MAKE THEM, YOU KNOW THE FUEL CELL PEOPLE.