There is an excellent answer to How do I add 1+1 using a quantum computer? that shows constructions of the half and full adders. In the answer, there is a source for the QRCA. I have also looked at this presentation.
I am still left with these questions:
What does a truth table for a QRCA look like?
What would a unitary matrix for a QRCA be?
What would a circuit diagram for a QRCA look like? (There is an example of a 6-bit circuit in the arXiv paper)
What would a circuit diagram for a QRCA look like? (There is an example of a 6-bit circuit in the arXiv paper)