Yes, you can go to a dual outlet muffler on your 99 SE. That is exactly what I, and many others, have done with our SE models. http://www.bonnevilleclub.com/forum/...ic.php?t=40304
But I disagree that you could make cutouts in your bumper and bumper cover to accommodate the tips, and still have it look good. I think the only reasonable way to do it, -and it'* what I did, -is just sling the tips under your existing bumper, and keep the rest of your car the same.
Otherwise, you will need a lot of mouldings to match up the sides with the bumper trim if you swap the bumper from a dual-outlet model.
You can play a bit with how far apart you want the tips to be, I requested my exhaust guy place them in the same location a dual-outlet Bonnie has them, and provided pictures.
97 SE, teflon wiper blades, Dunlop Sport A-2 tires, Leather steering wheel cover, Pioneer DEH-P480MP mp3 CDRW head unit, Pioneer 12-disc changer, iPod hookup, Boston Acoustic 3 way 6x9'*, Boston acoustic separates in door pods, Alpine 4 channel amp in trunk. Magnaflow dual outlet muffler and Ractive stainless tips. Autozone rice pipe and K&N 4750 intake kit. Clear corner lights. Energy Suspension end links.