Someone run out and test fit one of these:
http://www.sears.com/diehard-advanced-gold-agm-battery-group-size-94/p-02850793000P
I think it might just be one of the biggest that fits, not sure on the AH
rating but with the size it should be around 90AH. Specs show it at 12.4"
long, however it has protrusions on the ends for clamping down that could
easily be trimmed if necessary.
Karl