If you don't have the right hammer. Place a broomstick where you need to ding it and hit the broomstick with your regular hammer. This will give you a nice clean ding I the tubing. But you should be able to get it to fit without doing this. If not you would be the first person who has had fitment issues with these headers.
I would never grind my headers or steering linkage. How much clearance are you going to grind away on your headers before you put a hole in your primary pipe and I would never want to grind my steering linkage as small as it is to begin with. If I had to make clearance it would be much better to put a small dent in your pipe. But like it was said before, you just need to shift the motor over on it's mounts.