Check the Archives
There should be some articles in the archives on this. If not for the C-27, then for the C-30. The biggest drawback is the loss of headroom since you'll have to shim the floor so you can fit the wood to it. Without shimming, the floor is a compound curve and you can't bend plywood into a compound curve (curving in more than one direction). I'm assuming that you'll be using the plywood teak and holly flooring used in most production boats, including Catalinas. I'd check with a local boat builder for suppliers, or check out Wooden Boat magazine or their website.