I'm sorry that I put you to such effort based on a misunderstanding. By contrabass I wasn't making any reference to the instrument the double bass, but was merely the adjective meaning two octaves lower, the equivalent of a 32' stop on an organ.
The modern viola is, like the cello, tuned CGDA, but an octave higher. If an octave lower than a cello could be called bass cello tuning, then it could, logically if absurdly, also be called a contrabass viola tuning. (Cf a contrabassoon being an octave lower than a bassoon and two octaves lower than an oon.)
The tiny hint of humour in my post is now thoroughly extinguished by this verbiage, but never mind....