How to scuff up epoxy primer in order to spray the top coat?

I painted the underside of one of my Mopars with Nason Ful-Poxy 491-12 epoxy primer and then, dangit, life intervened and I didn't top coat it in a timely fashion (48 hours)! To make matters worse, the surface of the underside of the body is very irregular, with many flutes and louvers pressed into the body panels, so it will be relatively difficult to sand. The technical data sheet for Ful-Poxy says to sand it with 400 grit and then 600 grit before top coating it at this stage of cure. I have some questions for you body men: how about using Scotchbrite pads instead? Wouldn't that be easier than using sandpaper? What grade of Scotchbrite? Any suggestions about how to sand a highly-irregular surface like this the easiest way? Thanks very much.