Did some investigating on the Gibson tractor and I am going to have to make some more modifications to be able to mount the battery.  As this tractor seems to be made from a hodgepodge of parts from different models not everything fits right.  The rear implement lift bracket (spider bracket) does not sit level and is too high for the battery to fit under the seat.  When I get done this will most certainly be a 'Frankentractor'.  But it will work.