On a 75 even with a juvie ray you are looking at needing more filtration. A juvie ray would outgrow your 75 I am thinking within the year. I have never had Scobina nor have I seen one for sale local not sure how hard they are to come by. I have reticulata and have heard that they are not a hardy ray however I have had nothing but good luck with them. Then again they are in a 600 gallon system with excellent filtration and water change schedule

I wish you the best of luck, however I would say you are not ready for a ray yet, based on your tank size and filtration. These animals need more devotion and care than I think you are able to provide to them at this current moment. I commend you for doing some research though prior to getting into rays so many people do not.