Denting headers for clearance.

I lay an inpact socket on it's side and hammer against that to make smooth dents on headers.
I had to gain some clearance to install a heat shield between my headers and the valve covers(raised port heads). I used a hughmongous set of channel locks to squeeze the tube, would work great if u have the header off and heat it up some, just mark it first where it needs clearance. Also use a shim between the channel locks teeth and the tube , so as not to mark it . Better than beating them w/ a hammer !!