What, are you putting the other couple of pistons in or a new engine? ECTA allows running up in class, SCTA does not so the displacement does in fact need to go up to go from A to AA. A body class from, for instance, GC to ALT can be accomplished with some tape over the grill. If you have the ability to swap engines mid week, and of course some do, have at it and yes, paper work, pay money and re tech. Go for it!