1970 Duster Battery Size?

I know its an old post, but in case anyone else looks this up searching for batteries I've been using a group 27. It doesn't fit in the tray exactly, but the strap still fits over it to secure it(same width and height as the 24). It's just a bit longer but hasn't caused me any issues. But I did just replace it today with a 34 because I couldn't find a 24 with 800 CCA. I got an optima red agm, pricey but I've seen a lot of classic car drivers recommend them for longevity so I'm trying it.