Hey guys please help me out!

I'm busting a DIY for my HFC install on my sedan. I bought a used pair of crawford cats off of a member here, and was attempting to install them tonight.

Question: How much space do I need between the cats and the body of the car?
When I held the drivers side cat up, I noticed that they were practically touching the body. So I hammered away at the heat shield on the car to make space. I also did a little bit of work on the cat's heat shield. So far, I have less than a finger gap at the closest part between the cat and the body. Is it too close? Should I hammer some more? Will I damage the cats if I bang on 'em too much?