I don't think folks realize how low a bar Turing Complete is.
A DFA with two stacks or two counters is Turing Complete.
Making a formal machine Turing Complete is trivial.
Any textbook on formal languages and automata. Michael Sipser’s is my favorite. Church Turing Thesis is sophomore CS stuff..
Two stacks can simulate a Turing Tape. E.g. moving left is simulated by popping off one stack and pushing onto other. One counter can encode the tape while the other is used to encode the tape position.
