[bret]

There seems to be some manic obsession with running the tailpipes over the rear rearend housing. I suppose if you are working with a vehicle that is at or near stock ride height then pipes under the rearend would be visible and look a bit out of place. When the car is lowered significantly [like most of ours] the rearend is buried up into the car so far that those concerns go away.
If you look at the rearend housing position at full droop, [after the new suspension is installed], the mufflers are still lower than that level, so you have to go "up" to run them under the housing. The point is, they don't hang down or look out of place, and the routing is MUCH easier. I have been running them this way on the 48 Hour Camaro [and Velocity before that] for years.
Since our triangulated 4 link rear suspension does not intrude forward of the mufflers, most any brand of X pipe/muffler will be fine...and it will be a fairly simple deal to make tailpipes.