The headers I knew were suspicious on whether it was a full seal against the copper gaskets.
What I'm after it the actual diameter of the collars, something at the back of my mind says they are only about 2/3rds around the header pipe. So thought I'd ask the brains trust before I go all Jekyll & Hyde with the grinding.
Already had to heat the supplied ones and get a truer round on them

When fitted the edges are 'very' snug on the clamps and when I try to assemble them on the header there is no way that it will all come together.

My reckoning is that if the two studs pull up on at least 2/3rds of the diameter then a good seal should be gotten from the copper gaskets.