I've been running a modified repro of the factory 400 system with 2.25" pipes for a couple of years now, with a pair of resonators in the stock position and the dual inlet-outlet transverse crossflow muffler above and behind the axle. I like the sound, it's a low rumble at idle and maintains the low pitch at a slightly higher volume at higher rpms. The tailpipes exit under the trunk extensions as the originals did. No spacing of the X brace was necessary.
http://pg.photos.yahoo.com/ph/v_papesh/detail?.dir=39e3&.dnm=2451.jpg