Never done this before (no header gasket)

I think you'll end up with a big mess and leaks. But that's me. If you're worried about the clearance, I would pull that header back out and knock that corner in some on the shock tower. It's not like you ain't modded the body to get the headers through, so what's a couple more dents? I'd run some good gaskets if it was me. Just my friendly opinion.