I put an SLP Loudmouth on my 05 GT, I had a little bit of problem with alignment. Basically I just unbolted the brackets, put a couple of stainless washers under them here and there, and they fit pretty close. Of course with the Loudmouth, you can slide them in and out a little bit to adjust them too. Loudmouth's are kinda different than standard mufflers, not much muffle to them.:kooky:
I used a pair of work ramps and just backed the rear tires up on them, then braced the unibody with jack stands just to make sure it didn't fall on me and blocked the tires. Then I have a really big rug I slide under the car. Works pretty good.
The ramps are cheap too, I won mine in a raffle, but I think you can get a pair for $30 -$40. Mine are plastic and rated for 10,000lbs.