[joe117]

You need to have an acetylene torch to bend the 3/8" or 1/2" rods that need to be welded to the mufflers. These form the brackets that hold the mufflers to the rubber mounting points. You will need to be able to cut the old system apart, weld on the new mufflers to the old cats, weld the brackets, that you made, to the new mufflers, cut the bent, 3" turnouts and weld them to the new mufflers. All this has to be done just right in terms of length and angle in order to get the turnout to come out of the sidepipe cover hole. And remember, the sidepipe cover will be off, so you have to remember or mark somehow where the opening will be when it is in place. I was amazed when everything lined up on mine. It took all day.
As for performance, I'd say that good headers with a total high flow exhaust would probably only get you 35hp or so. Your installation, and mine, are somewhat less efficient than that and will probably give you less. Could you feel 20hp? I don't think so. At the drags it would probably give you .2 seconds. It's all for the sound in my opinion.
ps. I went to a Viper event one time and my car set off car alarms in two Vipers in the parking lot. Do you want to be louder than that?
I have no mods other than 3.55 gears.