Thanks fellas

Someone on another forum also mentioned hammering the muffler but yeh definitely not an option here..

PHO how much clearance did you have, just a rough figure from memory will do.. was it like a couple mm's or more like 1 finger gap?

I'm now leaning towards my exhaust system being the issue. When I bolted up the headers to cat I do remember now having to pull the cat towards the front..
Now I have to figure out how to create some sort of spacer between these donut flanges to line up the exhaust properly...