Yellow Tops are great, but do have a flaw (or at least did). If the car isn't used regularly (or the battery charged / used) then they can suddenly stop holding their charge. I had one in my last install and it provided admirable power for the system. You also have the added bonus they are sealed and you can mount them on their side if you need to.
As for size, I think it would fit. Not measured it myself, but think it would go. If not, there is another brand that I just can't remember the name of....