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I have added remote dual oil filters (not in a C5) but not a cooler. You can rough out what you need from the cooler size and hose size and lengths. In the end, it is the oil level that will dictate how much you need to add.
I have added windage trays in engines which allowed me to raise the oil level so I recalibrated/remarked the dipsticks. If you trust the dipstick mark and use that as your correct level you will be fine.
Good luck in racing. I need to get back in the game. I love hill climbs over everything.