very tight, one of my cats will vibrate against the crossmember at times, especially when turning left for some reason. I was afraid to try to push/slightly bend it off there, would only take prolly 1/8", but you know about header bolts, flanges, etc. So I stuffed a piece of high temp wrap 'tween 'em and problem solved...

 

The cat is actually about 9.5" (the top numers are in tenths) and thats after we opened them up to a 3" in/out so if you are planning on keepeing them at the 2.5" then you will need some more fab work to make them fit to the collector and that will take space. The max I think we could have moved the cats back towards the collector was maybe 3" +/-.

 

I think you may have solved some of my rattling issues I've been haing, I thought that there was a solid 1/2" between my cats and the crossmember but Im going to have to check it out since it only rattles when I really get on it