The melting point of zinc, the material/element used in galvanizing metal is 787F. Once burned you could remove the residue with a wire brush. Spending the extra money on stainless bolts can avoid the zinc concern if that bothers you. I use stainless steel bolts on my Webers not so much out of the galvanized concerns but for the clean up concerns. The stainless steel bolts clean a lot easier than the galvanized bolts.
I am not sure how much higher you want to elevate your cooking grate from its usual height. When cooking burgers or bacon using the indirect method, I will take another cooking grate and turn it upside down and place it on the first grate so the handles of the two grates are 12:00, 3:00. 6:00 and 9:00. This doubles the cooking capacity and the distance between the tops of the two grates is 2.25 inches. I hope some of this information helps.