New headers, new headaches

[n33k0]

I replaced the rusted and warped headers on my truck with new ones a few weeks ago. The new headers went in easy, and seemed to clear everything just fine, except for one spot at the passenger motor mount.

There is a tiny gap between the #2 primary tube and the motor mount, hard to see, but I can slide a credit card between the two, so it's not making contact (with the engine off). After driving around for a few minutes, I started to hear what sounded like metal vibrating on metal. I think it is the header rubbing on the motor mount (maybe it expands with the heat?)

I've read that shimming the transmission (TH350) at the crossmember can help move the header away from the motor mount. Is this true?

I know it is not the ideal solution, but I'd like to avoid getting another pair of headers (exhaust is already fabricated to fit these). I'd also like to avoid dimpling the headers, out of fear of ruining the ceramic coating.