Justin,
IIRC, the battery board was made of starboard on 245/250s, screwed down to the tops of the stringers. If so, 3/4" and plenty durable...
As far as hull thickness goes, you should see upwards of an inch about 12-18 inches away from each side of the keel, then it will drop down to 1/2"-5/8" out to the chines, then beef back up to at least 3/4" at the chines...
Been a while, you know...