You may want to check your engine specificatiosn befor installing it and creating more back pressure.
Move of those V8's call for dual 3" out and you may cause yourself more issues installing the muffler above.
You may need something like this.
This is what i did to my old shamrock as a fix and it worked well at slow speeds.
I used silicone turn downs, double clamped.
http://static.flickr.com/36/87782627_e900685110.jpg?v=0