OK. Since you appear to be going for a nice semi-gloss black underside, the scuffing will work fine. That isn't how I do it, but I am old and set it my ways. Just be careful about one thing! You need to THOROUGHLY scuff it. If you leave any shiny spots, those spots will NOT have 'tooth' or mechanical adhesion for the paint to stick to, and you will have problems down the road. Also, please note that like sandpaper, a piece of scuffing pad does not last forever. when it stops scuffing/cutting, switch to a new piece. and make sure you wipe/clean the scuffed surface down with a pre-paint cleaner and hit the surface with a tack cloth. Good luck, and POST PICTURES OF YOUR RESULTS.