You can use The Pool Calculator to calculate dosages, but what you wrote does not seem correct. To get to 50 ppm Borates, it would take 706 ounces of 20 Mule Team Borax (not 760 ounces, so was that a typo?) and 337 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) which is 2.6 gallons, not 14 gallons (where did you get that number?). The out of balance condition is relatively brief, but if you want to you can alternatively add one box (76 ounces) of 20 Mule Team Borax with 36-1/2 fluid ounces (about 4-1/2 cups) of full-strength Muriatic Acid. If you add the Borax first, then the pH may rise to around 8.3 while if you add the acid first the pH may drop to around 7.0 but the combination will keep the pH the same, say at 7.5 if that's what you started with. Just make sure to add slowly over a return flow at the deep end for best mixing and lightly brush the side and bottom of the pool after addition (especially after adding the acid).