One battery may light the thing off just fine, and nothing says the 2nd battery has to work or be connected if you just need ballast. Seems to me that A-bodies need all the rear weight you can put in there. I've seen as much as 300 lbs of ballast to get them to pitch rotate on a mid-10s car.
I've had good service from my Optimas but usually just buy batteries from Autozone, keep 'em on a Schumacher trickle-charger, and I get more than 7 years out of them and as much as 10. A load test (amps) is a better way to judge if the battery has enough grunt, but I've found if there's less than 12.4 static it's just about done for anything with decent CR or cyl pressure.