I just replaced 3 batteries in 3 of my classics. I went total cost saving, and bought 3 from Walmart for 69 bucks each. Group 34, top post, about the same size as a group 24 but the 34 is a touch shorter (goodie goodie..lol). The ones I replaced were from Farm & Fleet, couple went about 5 years and one about 2.5 years.
They whip them puppies right over... I think 600 CCA ??