I have no experience with Big Brandy F1, but Tomato Growers Supply describes it as RL indeterminate. Territorial calls it semi-determinate. Since they don't call it a dwarf or bush plant it's probably a normally sized plant.
If yours has the crinkly thick rugose leaves of a dwarf, I was expect it to stay shorter and more compact. If they are normal leaves, it will likely get fairly tall, though probably not as huge as a Brandywine.
Sounds like a nice cross, I'll be interested to know how you like it.
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Dee
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