You know the fighters. Match them at 175 and at Heavy. 15 rounds (not 10) for each bout. Fairly permissive rules, tho neither were particularly dirty nor cut prone. 20 foot ring. Moon in its waning crescent.
I think the moon would be crucial in this match, especially so if in its gibbous phase as we would be facing neap tides as opposed to spring, and this, i fear, would impact on Tunneys foot speed. I therefore favour Spinks.