Assuming 4.7 gallons of strike water (distilled), 3.7 gallons of sparge water (distilled), pre-boil volume of 7.4 gallons, post-boil volume of 6 gallons, and 5.5 gallons into fermentor (which is my actual system):
Added to strike water only: 2.8 grams gypsum, 2.8 grams calcium chloride, .35 grams canning salt, 7 ml of 10% phosphoric acid
Overall finished water profile, taking into account boil-off volume of 1.4 gallons:
63 ppm calcium
5 ppm sodium
59 ppm sulfate
76 ppm chloride
Estimated mash pH = 5.4
That's probably how I would brew the first iteration. Sulfate and chloride levels could be adjusted on later batches if necessary (maybe experiment with dosing glasses of the first batch with various amounts of gypsum and/or calcium chloride to see what changes; something I have never tried but keep meaning to).