Looking at the first page of the linked PDF, it's not explicit about whether the alphabet must be finite, although it's implied by the summary saying that addit

Looking at the first page of the linked PDF, it's not explicit about whether the alphabet must be finite, although it's implied by the summary saying that addition can only be done modulo some finite value. It is explicit about having an arbitrary alphabet, a single tape that's infinite in both directions and that the head has to move every time. I don't think I've ever seen anyone restrict a Turing machine in a novel way and not follow that up with a rigorous proof.