Do you already have a tuner you are working with?
Timing does not directly alter AFR in and of itself. However, by lengthening the burn time with added timing, you will lean out the fuel mixture. You will want to check the fueling after adjusting timing. You may not be in ideal timing now and there will be variables that you will want to verify with solid numbers. It will also depend on your octane and IATs how much timing you can safely add.