There is an optima battery that should fit, the 51R it is 9.25 x 5.0 x 9.0 (LxWxH)
What is the measurement on the stock battery? I measured the inside of the battery tray and i had 9.75"x6.75"x??.? I just don't remember the height, it should clear just fine, no cutting or anything.
There are more batteries here:
http://www.1st-optima-batteries.com/