I don't think you will need more magnesium, or any magnesium for that matter. Malt brings with it plenty of magnesium without the need for adding any more. I would drop the SO4 about 10 - 25 ppm and raise the Cl about 10-25 ppm, provided that you have the means to do that. You can also run the calcium up to 100 ppm with no negatives. Likely just fine as is though.