Looks like it's a 490CCA battery. From what I've ran into with my Kubotas the battery dementions is what gets you in trouble. My 3000 didn't have any room for anything bigger than stock. I got 11 yrs out of the factory Kubota battery. Might want to consider staying with original equipment.
You are correct, it looks like there are metal ears welded into the battery area that will only let a certain length battery be installed. That could be worked around if needed I believe but the battery would have to still fit between the hold down bolts. It looks like it could be wider and taller without a problem. I had a chance to look at mine very quickly since it was raining. I would like more CCA and reserve. I will get the dimensions and will visit the auto parts store to check to see what will fit. I have found out that it is a group 24 battery. Thanks for the help.
Not sure if it's the right size or not but Auto-zone lists a 24F-DLG that's 750 CCA and 130 min reserve. I had one of their gold series batteries and it did very well but it was in a car not a tractor.
I find it surprising that a 35hp tractor would have a 490cca battery, that seems pretty small. I have a regular full size pickup battery in mine, 850cca/1000ca, same as I use in my diesel pickup. I guess I'm lucky to have the room.