My dad ran a Ford V8 60 in his midget back in the late 40s. From his stories, you know how most old men embellish there stories with age, Heads and a cam would about double the 60 stock HP. He cut the bell housing off of the engine with a hacksaw and bolted a file on the end of the crank to machine back of the engine by hand to allow bolting on an in and out box.
I think a flat head belongs on a hot rod not in a Z. But if it is your dream, do it and send us the pictures of the Offenhauser heads and triple down draft carbs.