180/55 will be fine, but try to get a 70 ratio for the front as the profile seems to work better for the SS (depending on how your suspension is set up).
I run Diablos on road and race and love them. Not sure I would go with part worns though as you never know how many heat cycles they've been through. Remember supercorsas will be designed to go through less heat cycles than standard diablos before going off.
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