Don't worry about breaking the studs, they're better than grade 8 bolts. The problem might come when they are stuck in the heads, preventing lifting the head when the nuts are off. Sometimes you have to pull all the studs to get 'em off.
The 59A is the best flattie, with the possible exception of the Merc 255. When you get the heads off check real close for cracks. Don't worry about the one from the center water hole to the adjacent stud hole,they all do that and it doesn't matter. Any cracks in the valve seat area and cylinder walls do, though, and if the exhaust ports or valley have cracks, it's toast.
That's a truck 4-speed. That's maybe a good thing, because trucks were kept on the road longer than flathead cars, so the rebuild may be relatively recent. Rebuilders didn't mess with cracked blocks, so the chances are better that it's a goodie.