On injecting a turkey, 1.75 lb of Sweeter Than Sweet Cure to 1 gallon of water is perfect for an injection. For the cover brine then, you actually only need a 50% strength solution of the injection, so that would be 1.75 lb to 2 gallons of water (or 0.875 lb of cure per 1 gallon) and hold it in the cover brine overnight or 12 hours or so, then go to smoking!
If the cover brine is the full strength solution, same as the injection, it may be a bit saltier, but I don’t think you will ruin anything. You could add a little extra water for the rest of the soak too.
Good luck on the turkey and let us know if you have any other questions!