You want to know, if it will fit a car with 3" downpipe? Do you have a custom downpipe? Possible, but it may need spacers to clear the cat/or flexi, depends, how you your downpipe is made...
For example, it would fit that 3" downpipe - http://www.garaget.org/?car=249935&image=2402886 because there's no flexi and the cat is further back. I made it to fit that standard exhaust on the left.