Definitely have them put an h-pipe on and be sure to have them give you a way to disconnect the pipes at the muffler... or somplace before the rear axle. WHY you may ask?
The story...
I have a solid, welded 2 1/2" dual exhaust with h-pipe, and FM DeltaFlow 50's connected to Try-Y headers. I also have a Gear Vendors under/over drive unit. I just had to remove my tranny to change a front pump gasket (10 minute job). In order to remove the tranny I had to disconnect the exhaust from the headers (normal), but the h-pipe was in the way. Since the exhaust is fully welded, I had to remove the entire exhaust system. Of course it wouldn't go over the rear axle, so I had to remove the rear axle, which meant I also had to remove the slide-link traction bars, sway bar, rear shocks, rear brake hose, vent hose, and of course the drive shaft. Then I could start removing the overdrive unit & tranny... So a three hour job became a 3 day job, all because I didn't have a way to disconnect the exhaust pipes in front of the rear axle.... and I really didn't feel like cutting stainless steel pipes to make a shortcut for myself.
Good Luck Buddy!