That's not much room even if you swap to a 520 to allow for any slack. I know it seems more drastic, but if you are going to mod the brace, why not replace with with a wider arc piece (symmetrical on both sides) to accommodate the chain. I know that the brace is primarily to increase rigidity than structural integrity, but it seems like notching neuters it as a bracing device and makes it more cosmetic. Up to you though.