Don, if you can find room for it somewhere, one of the BIG 6 volts we used to use in banks of four on heavy duty Diesel road tractors will give you virtually unlimited cranking current. If you're still using the under the floorboard battery box, it would probably be necessary to fabricate a box that swivels down on parallelogram linkage to install the battery from underneath.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!