I dragged my sorry butt out to the truck and measured.
It looks like you are right about the group 1 6 volt.
I measured L:9 1/8, W:7 1/2, H:9 3/4
The length is going to be the determining measurement. I think it is plenty wide and plenty deep in the battery box, but 9 1/8 is really all I have. Maybe a group 25 or 35 would be better.
Thanks everyone for the info. I think I know where to go from here.
